
a Book _^ . 



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THE ELEMENTS 



OS- 



PHTSIOGEAPHY. 



SCIEl^CE CLASSICS, M^ pSJMEigCAPq ggg IIIE^LE-CLASS SCHOOLS 

BY 

JOHN J. PEINCB, 

Author of ''School Management and Method," etc., etc. 



FOURTH EDITION. -REVISED AND ENLARGED. 



;^/,,<^/4 



JOHN HEYWOOD, 

DEA:!srsGATE, AND RiDGEFiELD, Ma:n-che£tek; 

AND 11, Paternoster Buildings, 

LONDOX. 

IGSl. 



GfBss 



W lMamflf%r fr«m 

Fat. one* Lib. 

A»rl 1014. 



PREFACE, 



This little work has been prepared with, especial reference to the 
Syllabus for the Elementary Stage of Physiography — recently 
issued by the Science and Art Department — but not confined to 
it. It is hoped that it will be found useful to all who wish to 
inquire into the physical features of the earth, its atmosphere, 
&c. Ko efi'ort has been spared to render it accurate up to the 
information of the present day. 

To the student, I would say, to obtain a thorough knowledge 
of the Qonfiguration of the earth's surface, the superficial con- 
formation of the ocean, the currents thereof, and the course, 
tributaries, and water-partings of rivers, nothing short of a very 
careful study of political and physical maps (many good ones 
can be procured from the publisher of this present work) will 
enable him to succeed. 

J. J. P. 



COJSr TENTS. 



physics page, 

(including the elements of foece). 

Definition — Units of Time — Space — Mass — Metric System — 

Velocity — Force (composition and measurement of) 7 

Composition and Resolution of Forces — Parallelogram and Poly- 
gon of Forces 9 

Matter, — CompressibiKty — Elasticity 12 

Atteaction. — Gravitation — Cohesion — Chemical Af&nity — 

Energy produced by Heat, Electricity, &c 15 

Electricity and Magnetism. — Electricity — Electrical Disturb- 
ances — Atmospheric Electricity — Accumulation in the 
Clouds — Lightning — Thunder — Magnetis m 19 

Terrestrial Magnetism and Electricity. — The Earth as a 
Magnet — Mariner's Compass — Magnetic Elements — Mag- 
netic Storms — ^Aurora Borealis 22 

CHEMICAL ELEMENTS. 

Chemical Action — Compounds — The Chemical Elements — 
Atomicity — Binary Compounds — Terms — Compounds Bro- 
ken Up — Decomposition of — Rock-forming Minerals — Com- 
position of the Earth's Crust 26 

Water. — Composition of — Expansion of — Different States — 

Latent and Specific Heat 33 

GEOLOGY RELATING TO THE CRUST OF THE EARTH. 

Rocks. — Sedimentary — Stratified — Mechanically, Organically, 
and Chemically Formed — Surface Soil — Metamorphic — 
Unstratified — Plutonic 36 

Internal Heat of the Globe. — The Interior of the Earth — 
Phenomena and Distribution of Volcanoes — ^Hot Springs — 
Earthquakes — Earthquake Bands — Causes of Earthquakes 
and Volcanoes 46 

Crust of the Earth. — Upheaval and Subsidences — Relative 
Age of Strata — Changes of the Earth's Surface and in the 
Forms of Life— The Different Systems— The Age of the 
Earth 53 



Vi C0NTE2x'TS. 

ASTRONOMICAL GEOGRAPHY. page. 

Planets.— Form and Motions of — Sun and Moon — Day and 
ISTight — Seasons — Nutation — Precession of the Equinoxes — 
Eevolution of the Apsides 59 

PHYSICAL GEOGRAPHY. 

The Surface of the Earth. — Definitions 67 

Extent and Distribution of Land and Water. 

The Land : Mountains — Tablelands — Plains — Deserts 70 

The Ocean: Density — Weight — Depth — Composition — Colour 

— Waves — Tides — Currents 84 

Sea's Action upon the Crust of the Earth 93 

Waters of the Land — Springs — Rivers 94 

Table of River Systems — Lakes 98 

The Atmosphere. — Composition — Pressure — Height of — Baro- 
meter — Thermometer — Temperature , 104 

Winds— Trade Winds— Storms 110 

Vapour, Evaporation, and Condensation. — Dew — Clouds — 

Rain — Rainfall — Snow — Ice — Glaciers 115 

PheDomena of the Arctic and Antarctic Regions ,...,.-,r..r'r--T "^23 

Climate. — Causes Affecting it — Representation of i25 

Life and its Distribution. 

Horizontal and Vertical Distribution of Vegetation 128 

Distribution of Animals — Representative 132 

Distribution of Marine Life 135 

Distribution of Man 135 

APPENDIX. 

Light and Heat from the Sun 138 

PARALLAx^Distances of Heavenly Bodies 140 

Solar System — Planets — Satellites 142 

Comets and Meteors 146 

Fixed Stars 148 

Spectrum Analysis 151 

Latitude and Longitude 157 

Map Projections and Geodetical Surveys 159 

Instruments 164: 

The Nebular Hypothesis; or the Origin of the Earth 168 

Syllabus of Physiography issued by the Science and Art 

Department 173 

Examination Papers 174 

Index 186 



THE ELEMENTS OF PHYSIOGRAPHY. 



Physical Geography relates to the great natural features and 
arrangements of tlie globe regarding th.e land, water, atmosphere, 
and animal and vegetable life; but Physiography extends over a 
much greater scope, taking us into Chemistry and Geology to inquire 
into the nature of the materials of which the earth is composed, 
the origin of the different rocks, and their relative ages and history ; 
into Astronomy, regarding the earth as a member of the solar 
system; and into Physics, inquiring into the laws of gravitation, 
the electricity and magnetism of the earth, and into the effects of 
these forces. Hence we may conveniently treat of the subject 
under five chief heads, namely, Physics, Chemical Elements, 
Geology, Astronomy, and Physical Geography. 



PHYSICS 

(including the elementary principles op dynamics). 

Before considering the different forces which affect our planet, 
it is necessary that the student should possess some elementary 
notions of the action of force; and before we can measure its effects 
it is necessary that we should have some standard to compare with — 
hence certain units of measurement are adopted, namely, tmits of 
time, units of space, and units of mass. 

1. Unit of Time. — The mean solar day is the unit by which 
time is measured for ordinary purposes, it being the mean duration 
of a revolution of the earth upon its axis, or the interval of time that 
elapses between two passages of the sun across the meridian. This 
is divided into twenty-four parts, called hours ; these hours into 
sixty parts, called minutes ; and these again into sixtieths, called 
seconds. The second is usuaHy employed in mechanics as the unit 
of time. 



8 PHYSIO GEAPHT. 

2. Unit of Space.— The English unit of lenc;th is the Imperial 
yard, which is defined to be the distance between two marks on a 
metallic bar, kept in the House of Commons, when its temperature 
is 60° F. That this standard may not be lost very accurate com- 
parison has been made with the pendulum, from which it has been 
found that a pendulum in the latitude of London will vibrate or 
swing from the highest point on one side to the highest point 
on the other side in one second of time, and will always, under 
the same circumstances, have a constant length of 39'1393 inches. 
There are also certain copies of the standard yard kept in various 
places. 

The yard is divided into thirds, called feet ; and the foot into 
twelfths, called inches. The statute mile is 1,760 times this ^mit, 
and the nautical, or sea mile, nearly 2,029 — it being the length of 
one mean minute of longitude at the equator. Hence it is more 
suited for geographical and nautical measurements. 

3. Unit of Mass. — The English unit of mass is the Imperial 
pound, which is equal to a certain piece of platinum kept in the 
House of Commons, certified copies of which are kept in various 
places. It has also been found equal to 7,000 grains, one grain being 
^^^ of a cubic inch of distilled water at a temperature of 62° F.* 

4. In the Metric System of Length the base is the metre, which 
is defined to be the ten-millionth part of a quadrant of the earth's 
meridian from the pole to the equator, and equal to 39-3708 of our 
standard inches. This metre is divided into tenths called decimetres ; 
one-tenth of a decimetre is called a centimetre ; and a tenth of a 
centimetre a milUmetre. The centimetre, or the hundredth part of 
a metre, is usually called the unit of length; and the kilometre, or 
one thousand metres, is used for the measuring of longer distances. 
The unit of mass in this system is the gramme, which is defined to 
be equal to the mass of one cubic centimetre of distilled water at 
4°C. 

5. Measurement of Velocity. — Velocity is the rate at which a 
body moves or changes its position, and is always proportional to the 
force by which the body is put in motion — motion being the changing 
of position of any body. There are two kinds of velocity — uniform 
and variable — ^it being uniform when equal spaces are passed over 
in equal times, and variable when passed over in unequal times. 
Uniform velocity is measured by the space passed over in a unit of 
time, as one foot in one minute, or one mile in one hour, and so on, 
the greater the space and the shorter the time the greater is the 
velocity. 

* TMs is the pound Avoirdupois, the poiind Troy containing 5,760 grains. 



PHYSIOGRAPHY. 9 

If the space is given, and the time of the hody passing over it, the 
velocity mill he equal to the space divided hy the time. Thus, if a body 
move 15 miles in 3 hours, its velocity is 15-^3 = 5 miles an hour. 
The time of a body in motion may be found by dividing the space 
by the velocity, and the space by multiplying the velocity by the time. 

Variable velocity is measured at any instant hy the space tohich 
would he passed oxer in a unit of time, if the hody moved during that 
unit of time at the same rate that it had at the instant in question. 

Velocity is called accelerated when it moves over a greater number 
of units of length in each succeeding unit of time, and retarded 
Tfhen it moves over a lesser number of units of length in each 
succeeding unit of time. If the velocity is acceleratsd uniformly 
the space described in the given time is equal to half the space 
<io=.oribed in the first unit of time multiplied by the square of the 
time. 

6. ?orC3. — Force is that uMch causes motion, changes the direction 
of that motion, or causes it to cease. It is sometimes divided into 
two kinds, namely, external and internal, external acting upon 
matter at sensible distances, and internal, or molecular forces, acting 
only upon particles of matter at insensible distances — that is, which 
are too small to be measured. These again may be subdivided into 
attraction, repulsion, polar or magnetic forces, elasticity, animal and 
mechanical forces, &c. 

7. Composition and Eesolution of Forces.— It is usual in 

mechanics to represent forces by lines and numbers, the forces bear- 
ing the same proportion to each other as the lines or numbers do ; 
and if the lines are taken in the direction of the force, as well, they 
represent the magnitude and direction of the force. 

Any body that is acted upon by two forces would move as if urged 
by a single force whose magnitude and direction would be repre- 
sented by the diagonal of a parallelogram, the sides of which 
represent the magnitude and direction of the two forces. For 
example, suppose the body A in the annexed figure is acted upon by 
a force whose magnitude and 
direction are represented by A C, 
and at the same time by another 
force whose magnitude and dkec- 
tion are represented by A B, the 
single force represented in mag- 
nitude and direction by A D will ^^S- 1- 
produce exactly the same result if the other two forces were tak^'' 
away ; or if A D was reversed it would just balance or keep / 
equilibrium the two forces A C and A B.* J 

■* To complete tlic parallelogram draw C D equal and parallel toJ 
and B D equal and parallel to A C. 




10 



PHYSIOGRAPHY. 




This finding a single force which will produce the same effect as 
two others is called the composition of forces, the two forces being 
called the components and the single force the resultant. The inverse 
process— namely, of finding two or more forces that shall produce the 
same effect as one single force — is called the resolution of forces. 

8. Experimental Proof of the Parallelogram of Forces. 

Let C and B be two small pulleys, so constructed that the friction 
shall be as small as possible, and fastened to a vertical board ; also, let 

P, Q, R, be three forces, or 
weights, fastened to the ends of 
three cords of fine silk, the other 
ends being cai'ef uUy knotted at 
the point A; the weights will 
become in equilibrium, the point 
A being kept at rest by the 
three forces P, Q, 11 acting in 
the direction of the three curds. 
Along A C take A c equal to aa 
many units of length as there 
are units of weight in P, and 
^ A.a along A B equal to as many 
Fig, 2. units of length as there are units 

of weight in Q. Complete the parallelogram A c b a, producing 
the diagonal A b, which will be in the same straight line as A R, and 
containing the same number of units of length as R contains units 
of loeight, thereby proving the truth of the parallelogram of forces. 

Arithmetically — Let P = 161b, and Q = 121b., and acting at an 
angle of 90°, then Ac = 16 and Aa = 12 units of length. 

Hence the diagonal may be found thus, by Euclid L, xlvii, : — 
A62 = Ac2 +_Aa'^ = IG^ + ]22 = 256 +144 = 400. 
.-. A6 = V^OO = 20 = resultant of P and Q. 

If the angles are any other than 90° the resultant may be easily 
found by the use of the scale of proportionate parts. Thus, sup- 
posing the two forces are 41b, and 31b, respectively, and the angle 
60°:— 

Take any scale, say lib, to an inch, 

remembering, the larger the scale the 

more correct the answer. From the 

point A draw the two lines A C and 

A B, inclined to each other at an 

angle of 60° (which can easily be 

^^^" ^* done by the aid of the protractor), 

mark off A C = 3 inches, and A B = 4, complete the parallelogram 

A B D C. Draw the diagonal A D, which will be found to measure 





PHYSIOGRAPHY. 11 

a very little trifle over 6 inclies ; tlierefore the magnitude of the 
resultant is 61b. in the direction A J), the angle made by this with 
the line A B being 25-^.* 

In a similar manner we can find the components when their 
resultant and direction — that is, the angles they make — are given. 
Thus, giving the resultant to be 61b., and the direction which it 
makes x-espectively 30° and 45° : — 

From the point A draw the two lines 
A C and A B any length, inclined to 
each other at an angle of 45° + 30° = 
75^ ; thou produce A D, equal to 6 units 
of length, making an angle with A B 
of 30° ; draw C D and B D parallel to 
A B and A C. It is evident they will 
cut off the necessary lengths of the 
components. Fig. 4. 

9. Polygon of Forces. — When a body is acted upon by more 
than two f>'rces at the same time, we must take any two of them 
alone and find their resultant, and then take the resultant as a new 
force in conjunction with the third, find their resultant, and so on, 
whatever be the number of forces, 

10. The Eesilltant of any two forces is also always described 
by the thirtl side of a triangle, whose other two sides represent the 
forces in magnitude and direction. For instance, in Fig. 3, if we 
have given AC and CD, AD can be found without drawing the 
other two sides of the parallelogram. This is called the triangle of 
forces. By this method the resultant of a number of forces may in 
many cases be obtained more easily. When three forces act in the 
direction of the three sides of a triangle they will remain at rest. 

11. Velocities. — The method of composition and resolution of 
forces is also applicable to velocities. Thus, supposing a ball moving 
along a smooth horizontal floor, at a rate of four feet per second, 
is struck at a certain point in a direction inclined at 60° to its 



* By Trigonometry the solution is thus : Taking P and Q to represent 
the forces, and R their resultant— that is, A C = P, A B = Q = C D, and 
AD=R, ACD = 180° - C A B = 120°. 

.-. R2 = P2 + Q2 - 2PQ COS. 120° = ps + Q2 + PQ, since cos. 120' = - i- 

CD 

Hence R = -v/9+ 16 + 12 = 37 = 6-0S21b. and the direction of R = ^jy 

ein. 120°= -4^ sin. 120° = -^-^- = — 'ji— = -5695=34* 43' = angle CAD, 
v'S? 2v/37 37 

or angle BAD =-^ = 3JL60G95 ^ .^g^i = 25° 17' 
2xV37 74 



12 PHYSIOGKAPHT. 

original path, a velocity of 3 feet per second being communicated to 
it, the resulting velocity is found to be 6 feet per second in the 
direction A D (Fig. 3, page 10), by exactly the same consti'uction. 

There are the simple cases of forces and velocities requiring 
notice. If a body is influenced by two forces of 801b. and 601b., 
acting in opposite directions, its resultant force is evidently equal to 
201b. in the direction of the greater force ; but if both forces 
act in the same direction, its resultant is the sum of the forces, or 
1401b. In a similar manner resulting velocities are found. For 
instance, if a vessel is steaming along with a velocity of twelve miles 
per hour against the tide, which is moving at the rate of four miles per 
hour, the resulting velocity of the vessel is 12 - 4 = 8 miles per hour ; 
but if steaming with the tide its resultant would be 12 + 4 = 16 
miles per hour. 

MATTER. 

12. Matter is the name that has been applied to the earth, with 
the different substances upon it. It consists of minute particles, 
or molecules, which is the term now used to express the smallest 
portion of any substance that can exist in a separate state, but still 
containing groups of atoms, which cannot exist in a separate state, 
being indivisible. 

All matter is continually in motion, either as a whole or among ita 
particles, being acted on by certain forces, each of which has its own 
special properties. Thus, for instance, a stone, or other mass, unsup* 
ported falls to the ground, and would, if there was no resistance, 
fall to the centre of the earth. Or again, notice how rivers run down 
hill. There must be a force to cause the water to run at all, and 
this force is the attraction of gravitatien. 

There are generally three different states of matter recognised — 
EoUd, liquid, and gaseous. The force of cohesion being greatest in 
solids, less in liquids, and least in gases, (See " Cohesion," 19.) 

A body is said to be dense when the 'pores, or spaces between the 
atoms, are few, so that a large number of particles unite in a small 
mass ; and -porous when there are many pores, as sponge, &c. 

13. Compressibility.— Compressibility is the quality of being 
capable of being forced into a smaller space or compass. All solids, 
liquids, and gases are compressible ; though solids and liquids are 
very little in comparison with gases, except in very few cases. The 
compression of water at 50° F. has been shown by Canton, in his 
experiments, to be about 46 millionths of its volume, when the 
atmosphere is in its ordinary sta,te (2 9 J inches of mercury), alcohol 
being 66 millionths, sea w^ater 40, and mercury 3. 

14. Elasticity. — A body is said to be elastic when, after being 
bent in any direction, it tends to recover its shape if that force 



PHYSIOGRAPHY. 13 

which had altered its figure is removed ; and 'perfectly elastic 
when the force with which it tends to recover its original form, or, 
as it is called, the force of restitution, is exactly equal to the com- 
pressing force. In some bodies this resisting force of elasticity is 
greater than in others — steel, caoutchouc, cork, cane, &c., being very 
elastic. If we take a table-knife and bend it, it will return to its 
original shape unless it is distorted beyond the limits of elasticity. 
The reason it tends to recover its former shape is owing to tho 
exertion of two forces, namely, attraction between the partially- 
separated atoms on the out?ide of the knife, and repulsion between 
the closely-approximated atoms of the inside of the knife. 

When a body is drawn or twisted out of shape it is said to be 
strained — strain measuring the amount of deformation. For instance, 
if a piece of wire, or other substance, was stretched, the strain would 
be the elongation, or distance it had lengthened, divided by the 
length of the wire or other substance. 

Hooke's celebrated general of elastic forces is, the strain is pro- 
'portional to the stress that produces it, stress being the name given to 
the force or forces that tend to produce the elastic strain. Hence, 
after finding the strain, and dividing the stress by this, we obtain 
the modulus of elasticity for that particular material, or, if requned, 
we can reverse it and find the elongation, and so on. 

No kind of matter in a solid state is perfectly elastic, though 
many are in a high degree. To be perfect the force of restitution 
must equal the force of compression. Hence, the elasticity of any 
matter is the ratio that the force of restitution bears to the force of 
compression, or equals the former divided by the lattei". It has 
been found to be in glass, '94: ; ivory, '81 ; steel, "79 ; cork, '65 ; and 
brass, "41. Gases are the only states of matter that possess tho 
property of being perfectly elastic. 

ATTRACTION. 

15. Gravitation. — Gravitation is the tendency of all matter in 
the universe towards other matter ; or, in other words, any two pieces of 
matter have a tendency to approach each other, though in .'small 
bodies, or those of only moderate size, it is too feeble to be observed 
under ordinary circumstances, but in other cases it is presented 
strongly to us. For instance, notice how a large ship will attract 
boats, or a teaspoon in a cup of tea the bubbles on the top, &c. 

The weight or heaviness of bodies is due to gravitation, called 
terrestial, or apparent gravity — weight being the name we give to 
the efi'ect of gravitation or the measure of the attraction. Newton 
is said to have been the first who recognised the existence of 
gravity, and that by the falling of an apple. This same force 13 



14 PHYSIOGRAPHY. 

exerted on all the planets. For instance, the moon is kept in its orbit 
revolving round the earth by the attraction of gravitation of the 
earth ; the earth in its orbit round the sun by the attraction of that 
luminary ; the attraction being in all cases inversely as the squares of 
the distance of the lady from its centre of gravitation. Hence the force 
of attraction on bodies at the moon will be 60^ = 3,600 times less 
than on the surface of the earth, its distance being 60 times the 
earth's radius. In a similar manner any matter weighed at either 
of the poles would be heavier than at the equator, owing to the earth 
not being a perfect sphere — the equatorial diameter being 7,925 miles 
and the polar being 7,899 miles. This fact increases the weight at 
the poles by -^}j-^ over its weight at the equator. There is stUl 
another cause of the diminution of gravity at the equator, and that 
is the effect of centrifugal or, as it is sometimes called, centreward 
force in diminishing attraction, it being greatest at that place, 
and decreases as we get nearer the poles. As bodies at the 
equator in their daily motion move more rapidly than near the poles, 
owing to their radii being greater, a body taken from the poles to 
the equator loses through this force ^^ of its weight. Hence the 
total loss is about -^^ ; that is, a body of 1941b. at the poles weighs 
1931b. at the equator, -g-^-g- of ita weight, or h\o7s., being lost in 
consequence of its greater distance from the centre of the earth, and 
T^, or 10 Joz., in consequence of the centrifugal force acting there. 

16. The Intensity of the Attraction of Gravitation, 

or the Attractive Energy, not only varies with the distance of 
the bodies from each other but also with the mass of each body. 
Hence it is that the sun, the centre of the whole universe, is 
capable of attracting the most remote planets, though their distances 
are hundreds of millions of miles from that body, its mass being 
greater than all the other planets taken together. Hence we have 
the follovmig law : The force of gravitation between two bodies is 
'proportional to the product of their masses, and is inversely pro- 
portional to the square of the distance hettveen them. 

17. The Law of Terrestrial Gravity is as follows : The 

force of gravity is greatest at the earth's surface, and decreases 
v.2:)wards as the square of the distance from the centre increases, and 
downwards simply as the distance from the centre decreases, as, sup- 
posing a ball that weighed a pound on the surface of the earth to be 
taken do-vm. to the depth of half the radius of the earth, it is 
evident there would be the downward force from the earth below it 
and the upward force from the portion above it. Hence it would be 
influenced only by the difference between these opposite forces ; and 
as the downward attraction is t\dcQ as great as the upward, it will 
evidently exceed the upward force by half its original attraction, 
the other half being balanced by the upward force j that is, the ball 



PHYSIOGRAPHY. 15 

v7ould only weigli one haK poirad, and if taken to the centre of the 
earth it would have no weight at all, as the upward and downward 
forces will evidently balance each other. 

From what has been said on gravitational attraction, it would 
appear that all bodies are drawn towards the earth. Then what 
causes balloons, smoke, steam, &c,, to rise? It is the same force, 
namely, gravity. When a body is lighter than the air it will rise, as 
the air, being more strongly attracted, will get beneath it, and, dis- 
placing it, cause it to rise. In a similar manner cork, wood, &c., will 
not sink in water, owing to the same force. 

18. All bodies falling are acted upon by this force, though those 
of diflfereut material do not always fall through the same number of 
units of space as each other, or bodies of the same material but 
different in shape ; yet, were they let fall in a glass receiver with the 
air pumped out, their times and spaces would be exactly equal, 
showing that the difference in velocity is caused by the resistance 
of the air to the falling bodies, varying with their forms and 
dimensions. 

When a body falls the earth attracts it, so that it falls a certain 
number of feet in the first second of time, the body being then in 
motion with a velocity of say one unit. The earth still attracts it, 
and during the second second it communicates to it an additional 
unit ; so that in every successive second of time the attraction adds 
to its velocity in a similar proportion. Hence the spaces 
in each successive second are as the odd numbers 1, 3, 5, 7, &c. 

A body left free to move, and acted on directly by the force of 
gravitation, all resistances being excluded, will, in the latitude of 
Greenwich, fall through 16'09o4 feet in a second, thereby acquiring 
by this motion a velocity of 32'190S feet per second. This velocity 
is called the force of gravity, or acceleration due to gravity, and 
is represented by g. The space travelled over by a falHng body in 
one second is 16 feet 1 inch very nearly ; and the space described in 
t seconds = ^ gf^. If we know the time required for the fall of any 
body through a given space, the velocity with which it moves can 
easily be found, or vice versa. 

Formula. — Let v represent the velocity, t the time of descent, 
s the space described in the time t, and g as above. Then w^e have : — 

8=^gt^=x^l_ =x^t ; v=^gt= ^= ^J2^s ; s.ndt='^=^= ,/?i 
g t g V \l g 

If the body is projected upwards with a velocity v, then s = vt-\ 
gt^ ; and i£ downwards, s = vt-\-\gt'^ . 

19. Cohesion. — The attraction of gravitation causes a body when 
unsupported to fall to the ground ; but the attraction of cohesion 



16 PHYSIOGRAPHY. 

causes the particles to hold, together and unite in masses. When 
the cohesion exceeds the other forces we have a solid ; when the 
forces are equal we have liquid or fluid ; and when heat predomi- 
nates we have gas or vapour. For instance, take a piece of ice. Its 
particles are held together by cohesion ; but take it near a fire and 
it will soon melt ; the cohesive attraction being overcome by the 
repulsive power of the heat, its particles or molecules are driven 
asunder, and the ice becomes a liquid ; and now, by applying more 
heat, it is soon converted into steam, which on entering the cold air 
becomes a watery vapour. 

It is gravitation which brings the particles of matter close enough 
together for the attraction of cohesion to be exerted upon them, as 
in the case of sandstone and other rocks. When gravitation has 
finished its work — bringing the loose grains of sand together — • 
cohesion commences, and firmly unites these particles into a com- 
pact mass of sandstone. 

Heat and cohesion constantly act in opposition to each other. 
Hence, the more a body is heated the more its particles will be 
separated. The two may be noticed even in the efiect that tbey 
produce upon our bodies. For instance, on a warm day our flesh 
especially the hands and feet, swells from the efiects of the heat, but 
on cold days contracts, owing to the cold (or absence of heat) causing 
the particles to cohere more closely together. 

It is the attraction of cohesion that causes the small watery 
particles which compose mist or vapour to unite together in the form 
of drops of water, rain being thus produced. 

In the manufacture of shot we have a good illustration of the 
parts played by gravitation and cohesion. The lead for the shot is 
melted at the top of a high place or tower, then a little arsenic is 
added to give it the exact fluidity. Afterwards it is poured through 
a kind of sieve, throiigh which it passes by the effect of gravity — 
namely, its weight — and falls to the ground. In its descent it 
assumes the form of & sphere through the force of cohesion acting 
upon it. 

20. The strength of materials depends enth-ely upon the 
force of cohesion. The reason iron is so much stronger than wood ia 
the cohesion existing between the particles of iron is much greater 
than that existing between the particles of wood, owing to the 
difference in the degree of closeness of the particles, and the 
consequent changes in the effective action of gravitation. 

Wood is composed of layers, namely, one year's production of 
wood after another. Hence, its particles csnnob be so close together 
as in iron or any other metal, as their particles form a granular 
arrangement through beicg melted, which they are in nearly every 



PHYSIOGRAPHY. 17 

case before being used ; but even then the closeness and fineness of 
the particles vary much, being closest in steel. 

Matter is said to be hrittle if the cohesion between Its atoms is so 
limited in extent as to be overcome by a slight displacement, and to 
be tenacious when the attraction is so great that it requires a 
considerable force to overcome it. 

21. Chemical A£5.nity is that property hy which todies comhine 
and form new compounds and the power which causes them to continue 
in combination. It dififers from the attraction of gravity in not 
acting on masses, and only at insensible distances requiring bodies 
to be in actual contact. In this last property it resembles cohesion, 
or cohesive affinity, but differs from it by occurring only between the 
particles of dissimilar bodies. For instance, the particles in a mass of 
copper or sulphur are held together by cohesion, but if a particle of 
the copper comes in contact with a particle of sulphur they unite 
by the power of chemical affinity — the two particles being different — 
and form sulphuret of copper. 

In chemical compounds the proportion of the two substances is 
always definite. Thus when oxygen combines with hydrogen to form 
water, there are always eight units of the former to one unit of the 
latter, the molecules being united by chemical affinity, but held 
together by cohesion. The simplest cases of chemical affinity are 
those in which two bodies unite into a binary compound, being the 
result of single affinity, which power may be also exerted either 
between two elementary or two compound bodies. The force 
with which bodies chemically unite arises from mutual and equal 
affinity. Chemical combination produces some remarkable effiscts, 
often changing the form, colour, taste, density, and qualities — harm- 
less elements producing strong poisons, and strong poisons harmless 
compounds. 

Among the many agents that influence this affinity the chief are 
heat, light, electricity, proportion, &c. For instance, potash and sand 
unite under a red heat and form glass ; carbonic acid and lime are 
separated from marble or limestone by a red heat, &c. Light is also 
produced by chemical affinity. The majority of substances that 
give light are composed of hydro-carbon. The oxygen in the air 
first combines with the hydrogen, it having the greatest affinity for 
it. The carbon is then set free, and we have an intense light as the 
carbon passes from the hydrogen into the oxygen during the greatest 
evolution of heat caused by chemical combination. 

In order that chemical affinity may be thoroughly understood from 
the other forces of attraction we will give another example. If two 
particles of iron be brought in close contact they adhere close 
together by the force of cohesion, producing a larger mass, but still 
possessing properties in all respects identical with those of the par- 
B 



18 PHYSIOGRAPHY. 

tides of whicli it is composed. In a similar manner particles of 
sulphur may be made to cohere and form a larger mass of sulphur. 
But if the iron and sulphur be brought into contact the effect is 
different, as the mass so obtained is entirely distinct in its properties 
from either the iron or sulphur, being perfectly homogeneous, 
showing no traces of either of its constituents, and cannot be again 
separated into its elements by merely mechanical processes. This is 
an example of chemical affinity or attraction. It is requisite that 
all these characters be taken into accoiint to distinguish this affinity 
or attraction from cohesive attraction, because cohesion does take 
place between dissimilar particles, as when copper is plated with 
L^ilver by means of powerful pressure ; but here the mass is not 
homogeneous, and the silver and copper may be at once distinguished. 



ENERGY. 

22. Energy. — AU matter in motion possesses energy, or the 
power to do work. It is measured by the work it can perform. 
This energy cannot be destroyed, even by performing work, being 
only changed In form. A body may possess energy in one of two 
forms, namely, as kinetic energy or ^potential energy. 

Kinetic energy is that which is due to motion, and potential 
energy that which is due to what may be called a position of advan- 
tage, or, in other words, of an arrangement capable of yielding 
kinetic or actual energy, when there is nothing to stop it from so 
doing. 

Thus a moving mass — a bullet or cannon ball, for example — can 
do work in virtue of its nation ; a running stream by its motion 
works the mill, &c. Energy belonging to molecular motion, elec- 
tricity in motion, to heat and light, and actual chemical action, are 
included under the name of kinetic energy ; and energy due to 
absorbed heat, to electrical separation due to chemical separation, or 
due to being raised up to a certain position so that it ia capable of 
doing work in falling, &c., are included under the name of potential 
energy. To make plain we will give a few examples for illustration : 
A stone on being thrown vertically upwards has, on leaving the 
hand, sufficient power in store to raise it, though opposed to gravity, 
a certain height. Owing to the effect of gravity its velocity gra- 
dually becomes less and less, until its motion upwards ceases, its 
kinetic energy being now spent.* It now possesses the other kind of 
energy, viz., potential, owing to its changed position, thereby falling 

* Height it will rise = -^ where v = velocity in feet per second, and g = 
gravity =; 32-2 ; and this, multiplied by the mass = measurement of energj'. 



PHYSIOGRAPHT. VJ 

to the ground, and acquiring exactly the same energy as it had in 
starting ; but supposing the stone had lodged on some high 'building 
just as its upward motion ceased, it still would have had the same 
energy, in virtue of its position, but prevented from falling by tlea' 
building. 

23. Heat Produces Energy. — When the energy lies dormant 
in a body it is potential, but this can easily be turned into kinetic 
by applying heat, electricity, magnetism, &c. For instance, take the 
water, in a boiler, apply heat, and we soon have visible kinetic energy, 
viz., steam. 

Heat expands most substances, and in expanding or contracting 
they produce kinetic energy. For example, in laying rails on railroads, 
space is left between each joint for expansion ; if not, this force 
would tear them up out of the ground. Contraction produces 
equally as strong a force. It is taken advantage of by wheelwrights, 
coopers, &c. Thus the hoop or tire of a wheel is put on hot, then 
suddenly cooled, whereon it contracts with great force, binding the 
wheel and spokes firmly together. 

These very forces, looked into, explain such common occurrences 
as a cold glass vessel breaking when hot water is poured in, or a hot 
one when cold water is poured in, &c. 

To the heated state of the interior of the earth may be attributed 
volcanoes and earthquakes. 

Also, when a body is heated it exhibits energy in diminishing 
and increasing the powers of electricity and magnetism. For instance, 
in soHds a few degrees of heat will diminish the conductivity of 
electricity to a great extent, but in liquids, on the other hand, 
increase of temperature increases the conductivity. Again, an iron 
bar that has been magnetised suddenly loses the whole of its 
magnetism at a particular temperature. 

ELECTRICITY AND MAGNETISM. 

24. Electricity, like heat, lies dormant and concealed ia matter, 
giving no indications of its presence when in a latent state ; but 
when hberated is capable of producing the most sudden and 
destructive results. It may be called into action by friction, 
chemical action, heat, or magnetic influence. Its simplest form of 
energy may be seen in attraction and repulsion. Bodies charged 
with opposite kinds of electricity attract each other, and with 
similar kinds repel each other. A perfectly dry and clean piece of 
seaHng-wax, amber, or smooth glass, sharply rubbed with a dry 
woollen cloth, will, if applied at that moment, attract small pieces of 
paper, cork, &c., causing them to adhere for some time — the 
attracting body being now said to be electrified or excited. They 



20 PHYSIOGRAPHY. 

have also the power of communicating their electrification to other 
bodies ; and, again, a body electrified by either of them can electrify 
a third. 

There are various ways in which light may be produced from 
electricity. For instance, the sparks due to the discharge of electro- 
static accumulations from the clouds give an intense light — the 
most magnificent example being lightning. 

The greatest known heat with which we are acquainted is 
produced by the agency of the electric or galvanic current, as all 
known substances can be melted or volatilised by it. 

25. Positive and Negative. — As there appears a difierence 
between the kind of electricity excited by rubbing a piece of 
glass and that excited by rubbing a piece of wax or resin, Du Fay 
inferred from this that there are two kinds of electricity — the one 
vitreous, because especially developed on glass, and the other resinorjis, 
because first noticed on resinous substances. He supposed these to 
exist in equal quantities in all neutral bodies, and that when two 
bodies are rubbed one on the other they are separated. One of 
the bodies becomes overcharged with one of the fluids, and the othei 
with the other fluid — it depending on the nature of the bodies 
v/hich shall receive the excess of the vitreous and which shall receive 
the excess of the resinous. 

The theory that seems moat generally admitted now is that of 
Franklin. He is of opinion that there is but one electric fluid, 
which possesses an attraction for various substances in various 
degrees, and that every body in its natural condition is associated 
with a certain quantity of this fluid. When two bodies are rubbed 
together friction causes some of the fluid to leave one body and pass to 
another, whereupon one becomes overcharged or positively charged, 
and the other undercharged or negatively charged. Hence the terms 
positive and negative. 

28. Electrical Disturbances. — Telegraph lines are constantly 
troubled by electrical disturbances, called earth currents. They are 
frequently so powerful as to render the use of the instrument 
impossible for some time. These disturbances are found to be very 
closely connected in some way with the perturbations of terrestrial 
magnetism called magnetic storms, which are also closely connected 
with the aurora boreaHs and sun spots. 

27. Atmospheric Electricity. — The atmospheric medium by 
which we are surrounded contains not only combined electricity, the 
same as every form of matter, but also a large quantity of free and 
uncombined electricity, sometimes being positive and sometimes 
negative, but generally the opposite kind to that of the earth. 

Various kinds of apparatus have been contrived for the examina- 
tion of the electric state of the atmosph»;ie, such as poles elevated 



PHYSIOGRAPHY. 21 

about thirty feet in the air, and being provided with a metallic point 
at their upper ends, and insulated at their lower ends. 

By the aid of these instruments it has been found that, in clear 
weather, signs of free positive electricity are always present in the 
atmosphere, it being weak before sunrise, but gradually gets stronger 
as the sun passes the horizon, and soon afterwards gains its greatest 
strength ; it then rapidly diminishes, and regains its minimum state 
some hours before sunset, after which it again increases, gaining its 
second maximum state, then decreases until the following morning.* 
It has also been noticed that the electricity of the atmosphere 
increases from July to January, then decreases, being more intense 
in the cold weather. 

28. Accumulation of Electricity in the Clouds.— The 

chief sources from which the clouds appear to obtain their electricity 
are evaporation from the earth's surface, the chemical changes which 
take place on the earth's surface, together with the expansion, 
condensation, and variation of temperature of the atmosphere and 
its moisture. 

29. Lightning and Thunderstorms.— When a cloud over- 
charged with the electric fluid approaches another which is 
undercharged the fluid rushes from the former into the latter. This 
discharge produces the vivid flash known as lightning, accompanied 
by the sound of thunder, which is similar to the report of a gun 
when discharged or fired. When successive discharges of the 
accumulated electricity take place it causes great disturbance in the 
air, thereby causing thunderstorms. The air being suddenly rarefied 
and dispersed, in the course of the lightning, rushes together again 
after the discharge has passed. In this way the air is perhaps 
disturbed for miles at the same time. 

The most dreaded of lightning is what is sometimes called the 
returning stroke, as the earth containing positive electricity, or being 
overcharged, returns its overplus to the clouds. The flash of 
lightning always proceeds from a positive body — that is, one which 
is overcharged with electric fluid. 

From observations made in Saxony, and Kremsmunster, in Bavaria, 
the conclusion has been arrived at that there is a periodicity in 
thunderstorms as well as in other natural phenomena. Thus, accord- 
ing to Von Bezold, in years when the temperature is high and the 
sun's surface relatively free from spots, thunderstorms are abundant. 
It has also been observed that the maxima of the sun spots coincide 
with the greatest intensity of auroral displays. It follows that both 
groups of phenomena, thunderstorms and auroras, to a certain 
sxtent, supplement each other, so that years of frequent storms 
correspond to those of auroras, and vice versa. (See 36.) 

* Becquerel Trai6, t. iv., p. 84. 



22 PHYSIOGRAPHY. 

Thunderstorms are very beneficial. They purify the air by pro- 
ducing nitric acid and ozone, which dispel noxious vapours, and by 
agitating the air stir up fresh currents of air or breezes, thereby 
causing it to be more healthy and pure. 

30. Thunder. — Several explanations have been put forth as to 
the cause of the noise that we call thunder. One is, that it owes 
its origin to a sudden displacement of air caused by the discharge 
of electricity which produces the lightning ; another is that the 
passage of the electric current causes or creates a vacuum, which the 
air rushes in to fill up, thereby producing the sound. 

31. Magnetism is the name given to the peculiar property 
possessed by certain bodies, especially iron and its compounds, 
whereby, under certain conditions, they mutually attract and repel 
each other. 

There appears to be two species of magnetic power — ^the northern 
and the southern — which are perfectly similar in their mode of 
action, but directly opposite in their effects. For instance, take two 
magnets, and it will be found that the two north poles (see 33) 
always repel each other, and the two south ones likewise ; but the 
north pole of one magnet invariably attracts the south pole of the 
other, or the south pole the north. Hence between like powers 
there is repulsion, and between unlike attraction. 

If a bar of mallaable iron is placed near the poles of a magnet it 
will become immediately magnetic, either with or without contact. 
This is called inductio7\ Each pole of the magnet induces the 
opposite kind of polarity in that end of the iron which is nearest to 
it. This bar of iron has now acquired the power of inducing a 
similar state of magnetism on other iron near it, and also reacts 
upon the magnet from which it first derived its power, iuca^asing 
the intensity of its magnetism. 

It has been found that the attraction and repulsion existing 
between two magnetic pai'ticles are always inversely as the square of 
the distance, thereby agreeing mth the law observed in electricity, 
the force of gravity, and every other known force proceeding from a 
centre in right lines. Coulomb introduced the theory of two 
opposite magnetic fluids, viz., a boreal fluid and an austral fluid, and 
that the magnetic body consists of small particles. The fluids, in 
their activity, are separated in each such particle, but never pass 
out of it. The amount of magnetic action is to be calculated as the 
accumulation of the magnetic forces of the several particles — that 
is, as the statical resultant of all those forces. It is necessary to 
remember, in Reference to a magnetic bar, that the terms ioreal, 
southern, and positive, all refer to that pole which would point 
towards the south, and austral, northern, and negative, to that which 
would point towards the north. 



PHYSIOGRAPHY. 23 

TERRESTRIAL IMAGNETISM AND ELECTRICITY. 

32. ThG Earth itself may be regarded as a spherical magnet, 
whose north pole corresponds to the south pole of an ordinary- 
magnet, and its south pole to the north. The cause of the earth's 
magnetism may be on account of the crust being largely composed 
of iron and other magneticable metals ; or, perhaps, due to the- earth 
currents moving from east to west around the earth, as the succes- 
sive parts of the earth face the sun. 

Dr. Faraday was of opinion that the magnetism of the earth is 
the result of the induction* of the electric currents ; or, if a 
terrestrial magnet really exists, its poles are close together near the 
earth's centre. 

33. Blariner's Compass. — A magnetic bar, balanced, by being 
fixed at its centre of gravity on a pivot, will, if free to move, after a 
few oscillations, assume a constant position, one end pointing to the 
north, hence called the north pole of the magnet, and the other end 
to the south, called the south pole. This is the principle of the 
mariner's compass, which guides the sailor when all other indications 
of this course fail him. 

To account for this property of the magnetic needle the earth is 
supposed to be or to contain an enormous magnet, the poles of 
which correspond very nearly to the geographical poles of the earth. 
According to Sir J. C. Ross the north magnetic pole is situated in 
lat. 70° N., long. 97° W., and the southern pole in lat. 75° S., long. 
184° E. 

The magnetic needle does not point exactly north and south. 
Hence the magnetic meridian does not coincide with the geographical 
meridian ; or, in other words, the north-seeking pole of the magnet 
does not agree with the geographical north pole. The difference 
between the two is called the declination, or magnetic variation. It 
is measured by taking the angle made by two vertical planes, one 
passing through the earth's axis and the other through the needle. 
At London the north-seeking end points about 17° west of north. 
The magnetic needle, when suspended on an axis at its centre of 
gravity, does not maintain its horizontal position — its austral or 
northern-pointing end dipping considerably in our hemisphere, and 
in the southern the opposite pole incHnes. This is called the dip 
or inclination of the needle, the needle being called a dipping needle 
or inclination needle. The inclination in this latitude to the horizon 
being about 70°, it undergoes periodic variations, though small in 
comparison to the declination. 

Lines passing through places having the same declination are 
called isogonal lines, and lines connecting places where the dip is the 
same are called isoclinals. 

* Induction is the production of like effects in bodies near to one another. 



24 PHYSIOGRAPHY. 

Observation has tauglit us that the magnetic poles change their 
position gradually during long intervals of time, and that they 
coincide with the points where the greatest degree of cold is felt or 
where the mean of the thermometer for the year is lowest on the 
surface of the earth. 

Besides this change, there is the daily variation in the magnetic 
needle, which commences about midnight or shortly afterwards. The 
north-seeking pole moves to the east. At about seven or a quarter 
past it is found to be 6' or 7' from its m.ean position. It then 
returns, passing the mean magnetic meridian about ten o'clock, 
reaching its greatest deviation — probably 3° from the mean — between 
one and two in the afternoon. It now starts towards the east, 
passing the mean at about five or six o'clock, still continuing to 
move slowly on till ten or eleven, when it moves so slowly as to be 
insensible for some time. 

It is believed that the sun is the principle agent in causing the 
variations. Professors Christie and Barlow, from experiments and 
observations, were led to the conclusion that the daily motion was 
dependent upon the relative position of the sun with respect to the 
magnetic meridian, and that the proximate cause was to be traced 
in the altered distribution of temperature. 

There are still other variations — namely, monthly and yearly — 
which may be called solsticial variation, but very little definitely is 
known respecting them. 

34. Magnetic Elements.— In determining the state of the 
earth's magnetisfh at any place, and at any time, there are three 
things to be observed, viz., the magnetic declination, the magnetic 
inclination, and the total force, or intensity. The declination and 
inclination are explained above. The total force, or intensity, is a 
number which expresses the force of magnetic attraction at the 
place and in the direction of the dipping needle. It is properly 
expressed in absolute units of force. Sometimes the horizontal 
force is given instead of the total iuteasity. The latter is derived 
from the former, by multiplying it by the secant of the angle of the 
dip." 

A unit of magnetism is usually defined as follows : A magnet is 
said to have a unit of free magnetism when it fulfils the following 
conditions : Let the magnet be free to turn in a horizontal plane, 
and at the same time, in the same plane, let there be another 
magnet, precisely similar and equally magnetised, at right angles to 
it, and opposite its centre, at a distance of one millimeter from it, 
then the former magnet has one unit of magnetic force if it tries 
to turn round with a force equal to that which would be exerted 
by a force of one milligram acting at right angleia to an arm one 
millimeter in length. 



PHYSIOGRAPHY. 25 

The magnetic elements for 1876 at Greenwich were as follow: 
Declination, or variation of compass, 19° 8' W. ; inclination, or dip 
of the needle, 67° 39' ; horizontal force, in British units, 3"9 ; total 
force (1873), 10-27. 

35. Magnetic Storms. — From observations in various parts of 
the globe the occasional occurrences which have been termed 
magnetic storms have been noticed. During these storms the 
magnetic elements — ^namely, the declination, and the amount of its 
horizontal and vertical components — are subjected to violent changes, 
which appear, frequently at the same time, over immense tracts of 
the earth's surface. For instance, a disturbance which occtirred at 
Toronto, in Canada, was found to agree precisely in time and very 
nearly in amount with a simiHar disturbance registered at Greenwich. 

From registrations taken at Greenwich and Toronto the occurrence 
of aurora borealis has been found, in nearly all cases, to be accom- 
panied by magnetic disturbance at both places. It has also been 
proved that the magnetic storms are in some way or other connected 
with the spots of the sun. Schwabe, of Dessau, shows that the 
various epochs of maximum spot frequency are also those of 
maximum magnetic disturbance of our globe. It is a remarkable 
fact that when a spot is forming on the sun our magnetic needles 
are unusually disturbed. 

36. Aurora Borealis, or Northern Light— So called because 

they appear in the north. They are flashes of light of various 
colours, sometimes taking the form of a dark segment, or of an arch 
or crown, and sometimes in the form of luminous streamers. They 
are frequently seen in the North of Europe, and of late years not 
unfrequently seen in this country. The cause of them is supposed 
to be the passage of electricity through the higher regions of the 
atmosphere, where it is highly rarefied. 

It has been calculated that its probable height is usually between 
seventy and eighty miles. Hence the density of the atmosphere 
would only be about the one hundred and fiftieth part of that at 
the earth's eurface. 

Several other reasons have been put forth at different times to 
show the cause of these lights, nearly all agreeing that it is within 
the region of our atmosphere. Heli ascribed it to the reflection of 
the sun and moon by the clouds of snow and needles of ice which 
continually float in the polar regions. Bailly ascribed it to 
magnetism, it being remarkable that magnetic disturbances have 
generally been noticed at the same time. Frankhn attributed it to 
electricity. Kastner was of opinion that the polar Hghts are the 
electricity of the earth rising periodically to the poles. 

Similar occurrences have been seen at the south of the Southern 
Hemisphere, but not so frequently. They are called aurora australis, 



26 PHYSIOGRAPHT. 

If an oval is drawn round the North Pole, passing through Iceland, 
the North Cape, Gulf of Obi, Northern Siberia, the mouth of the 
Mackenzie Eiver, the centre of Hudson's Bay, and Nain, it includea 
the region where the greatest number occur, averaging about forty 
annually. 



CHEMICAL ELEMENTS. 



37. ChGinical Action is the name applied to those operations, 
whatever they may be, by which the weight, form, solidity, taste, 
smell, colour, and action of substances become changed, forming 
new bodies, with different properties from the old. For instance, if 
we take some water and mix with it sul]Dhuric acid chemical action 
takes place, and the two cold liquids produce intense heat ; if we 
pour cold water on lime there arises heat from it, by the chemical 
action ; or if we take 56 grains of iron and 32 grains^of sulphur, 
chemical action takes place, the two substances forming ferrous 
sulphide (siilphide of iron), which differs in appearance and properties 
from both iron and sulphur. 

Chemical action assists the formation of rock masses, acting thus : 
First, the deposit becomes dry and contracts. It is then covered 
over with fresh layers, and exposed to great pressure, and also to 
an increased temperature, owing to the greater depths, the water 
carrying in chemical solutions (which arise from the water passing 
through the earth and coming into contact with many different 
minerals and substances) aU the time from one layer to the under 
or lower ones. 

Chemical action generally produces a change of temperature or a 
change of state, and often a change in colour. 

38. Compounds. — Tk^ \s>^^ assording to which chemical sub- 
stances combine and form compounds are very simple. The first 
and chief is that a compound is perfectly homogeneous, and that its 
composition is fixed and invariable. 

From experiments we learn that if a quantity of hydrogen, for 
instance, is taken and tried to make combine with bromine or 
chlorine we must take 79"75 times its weight of bromiae, or 35*5 
times its weight of chloriae, as they cannot be made to unite in any 
other proportion. Hence if we see any substance that can be recog- 
nised by its external properties as a compound of hydrogen and 
bromine, we are certain that its constituents are in the proportion 
of 1 to 7975 ; oe if the compound is of hydrogen and chlorine, 
those elements will be in the proportion of 1 to 35 "5. 

Again, suppose we take potassium and bring it in contact with 
the latter compound, viz., hydrogen and chlorine, it will at once 



PHYSIOGRAPHY. ST 

expel the hydrogen and unite with the chlorine, forming a compound 
of potassium and chlorine, taking 39 "13 parts of potassium to replace 
the one part of hydrogen. By similar experiments it is found that 
23*05 parts of sodium satisfy the affinity of 35 '5 parts of chlorine, or 
107*94 parts of silver can replace the 39*13 parts of potassium. In 
this way there could be obtained for each of the elements a number 
expressing the quantity of it that will satisfy the affinity contained 
in one part of hydrogen. These numbers, expressing the proportion 
in which the elements combine, represent also the relative weight 
of the atoms of which the different kinds of matter are composed. 
For instance, an atom of chlorine equals 35*5 times the weight of 
an equal volume of hydrogen. The weight of an atom of chloriQe 
being 35*5, and an atom of hydrogen 1. Hence the term atomic weight, 
the atoms being all the same size, with one or two exceptions, namely, 
phosphorus and arsenic, whose atoms are supposed to be half the 
usual size, and mercury, zinc, and cadmium, whose atoms are twice 
the size. An atom is the least part of an elementary body which 
can enter into or be expelled from a compound. 

39. Chemical Elements. — When the different substances 
found at the surface of the earth are submitted to various methods 
of treatment, the majority of them can be broken up into several 
substances of a more simple nature. Thus a piece of flint can be 
separated into two substances entirely different from it in appearance 
and properties, wood and chalk into three, alum into four, and so 
on ; while others, as iron, gold, copper, sulphiu*, &c., resist all the 
processes to which they have as yet been subjected, and appear to 
consist of only one kind of matter. It has been found by submitting 
all the rocks, minerals, animal and vegetable substances, &c., to 
appropriate processes, that they contain about sixty-five substances, 
by the union of which all the different kinds of matter are made. 
These sixty-five substances are called the chemical elements. The 
following is a list of them, with their symbols and atomic weights, 
that is " the proportions in which they combine among themselves." 
N^o combinations can take place among the elements Ojsly in these 
proportions, or multiples of them : — 



Atomic 
Names. Svmbols. Weight. 

a Hydrogen ...H i 

a Chlorine Cl 35*37 

a Bromine Br 79*75 

a Iodine I 127 

a Fluorine F 19 

Potassium ...K 39*13 

Sodium Xa 23 

Lithiurn L 7 

Caesium Cs 133 



Atomic 

Names. Symbols. "Weight. 
Eubidium Rb 85*4 

Silver Ag 108 

Thallium Tl ......204 



Oxygen .. 


....0 .. 


... 16 


Barium .. 


...Ba .. 


...137 


Strontium .. 


....Sr . 


...87-5 


Calcium 


...Ca .. 


... 40 


Indium 


....In .. 


...113 



28 



PHYSIOGRAPHY. 



Atomic 
Names, > -:.^-6ymbols. Weight. 

Magnesium -Mg 24-4 

Zinc Zn 65 

Cadmium Cd 112 

Copper Cu 63-5 

Mercury Hg 200 

Glucinium G 9-3 

Didymium D 96 

Lanthanium ...La 92 

Yttrium Y 61-7 



a Boron B . 

Gold Au. 



. 11 
.196-7 



Atomic 
Names. Symbols. Weight. 

a Nitrogen N 14 

a Phosphorus... P 

Arsenic As 

Antimony Sb 

Bismuth Bi 

Vanadium V 



31 
. 75 

.122 
.208 
. 52-5 



a Sulphur S 32 

a Selenium Se 79*4 



Carbon C 12 

Silicon Si 28 

Aluminium ..Al 27-5 



Zirconium Zr 

Thorium ...... Th 

Tantalum Ta 

Niobium Nb, 

Tin Bn 

Titanium Ti 

Lead PI 

Platinum ...Pt 

Palladium Pd 



. 89-5 

.116 

.138 

. 97-5 

.118 

. 50-4 

.207 

,197-3 

.106-5 



Tellurium Te . 

Chromium Cr . 

Manganese ...Mn. 

Iron (Ferrum)..Fe . 

Nickel Ni . 

Cobalt Co . 

Cerium Ce . 

Uranium U . 

Tungsten W . 

Molybdenum . . .Mo . 

Rhodium Ro . 

Ruthenium Ru . 

Iridium Ir . 

Osmium Os . 

Gallium Ga , 

Lavoesium La . 



.128 
. 52-5 
. 55 

. 56 

. 58-8 

. 58-8 

. 92 

.240 

.184 

. 92 

.104 

.104 

.197 

.199 



The elements marked (a) are non-metallic, the remainder t)eing 
metallic. The most important of the eleme^nts are printed in black 
type. 

40. Atomicity. — The elements have also diflFerent powers of 
combining. For instance, one atom of CI (see table) can only com- 
bine with one atom of H, but an atom of can combine with two, 
N with three, and C with four atoms of the same element H. Hence 
an atom of has the power of replacing, or is equivalent to, two 
atoms of CI, an atom of N to three, an atom of C to four, of the 
same element, &c. In a similar manner an atom of nitrogen can be 
substituted for five, tin for four, iron or cobalt, for six of any monad 
element — as hydrogen. 

Those elements whose atoms are equivalent to one atom of hydro- 
gen are called monads j those whose atoms can replace two atoms of 
hydrogen, dyads ; those whose atoms can replace three, triads ; four, 
tetrads ; five, pentads; and six, hexads. In the above table those in 
the first group are monads; second group, dyads; third group, triads; 
fourth group, tetrads; fifth, pentads; and sixth, hexads. 



PHYSIOGRAPHY. 29 

The symbols annexed to each element are letters tised to denote 
them without writing their names in full. In most cases the initial 
letter of the common or of the Latin name is used. This symbol 
also expresses, by remembering or referring to the atomic weights 
of the substance, the quantity by weight of the substance entering 
into combination. For instance, CI not only denotes an atom of 
chlorine but an atom consisting of 35"5 parts by weight of that 
element ; N, an atom, or 14 parts by weight, of nitrogen ; and so on. 
More than an atom of an element is expressed by a small figure 
placed below the symbol on the right, as CI2, the figure denoting 
the number of atoms. 

41. Binary Compounds are composed or formed ly the union of 
dements — namely, in the proportion of their atomic weights — as for 
instance, sodium and chlorine unite and form the compound sodic- 
chloride, having properties entirely different from either of the 
elements — there being 23 parts sodium and 35*5 parts chlorine. 

The symbols of compounds are formed by the juxtaposition of 
those elements. Thus, HCl represents one atom of hydrogen 
combined with one atom of chlorine, forming hydrochloric acid. It 
also further expresses the fact that the compound hydrochloric acid 
is formed of 1 part of hydrogen and 35*5 parts of chlorine. 

The rock-forming naiuerals of this class — viz., binary compounds — 
are few in number, the principal of which are rock salt and quartz. 
The chemical formula of rock salt is NaCl (chloride of sodium), 
that is, one atom of sodium combined with one atom of chlorine. 
It is mostly contaminated by a small quantity of extraneous sub- 
stances. The analysis of the Cheshire rock is as follows : Chloride 
of sodium, 98'32 ; of magnesium, "02 ; of calcium, '01 ; sulphate of 
lime, '65 ; and insoluble matter, 1. 

42. Terms, &C. — ^We will now give a short explanation of a 
few chemical names given to compounds, &c. 

Acids. — An acid is a compound containing a certain quantity 
of hydrogen, easily replaceable by a metal when it comes 
in contact with it, either in the free state or as an oxide. It has 
also, generally, the property of changing vegetable colours to red. 

Bases are compounds which, by reacting on acids, yield salts. The 
most important are oxides of metals. When brought in contact 
with an acid their oxygen combines with the hydrogen of the acid 
to form water. 

Silicates. — A silicate is a combination of an acid with one single 
base, when it is called simple ; or the acid is united to two or more 
bases, being then called compound. Minerals of this character — 
namely, silicates — are the principal constituents of rocks. 

Oxides are compounds formed by the union of oxygen with other 
bodies. 



30 PHYSIOGRAPHY. 

Peroxide and Protoxide. — When a substance unites with oxygen 
in two different proportions, that which contains the greatest quantity 
of oxygen is called peroxide, and that which contains a less quantity 
a protoxide. 

Suboxide. — Many metals have the power of uniting with oxygen 
in more than the above two proportions. In this case the com- 
bination which contains a less quantity of oxygen than the protoxide 
is called a suboxide, and the highest combination of the substance 
with oxygen is called a hyperoxide. 

Su'phides are compounds of the metals with sulphur, and form a 
very important class of compounds, presenting many analogies with 
the oxides. They are obtained either by heating the metals with 
sulphur in proportions, or passing a current of hydrosulphuric acid 
gas through a solution of salt. The sulphides of the metals of the 
alkalies and alkaline earths are soluble in water, but of other metals 
insoluble. The sulphides are a very important class of compounds, 
forming some of the most important ores from which the metals 
are extracted. 

Pyrites. — The name given to the sulphide of iron. 

Alkalies. — An alkali is a body that possesses properties the 
converse of an acid. It has a highly bitter taste ; changes the blue 
juices of vegetables to a green, or the juices of vegetables which have 
been changed red by an acid back again to blue. Potajsh and soda 
are representatives of this class. 

43. Compounds broken up into Simpler Forms.— As 

before stated, there are about 65 elementary substances. Of these 
only 17 occur extensively amongst mineral compounds. They are 
oxygen, hydrogen, carbon, sulphur, chlorine, fluorine, silicon, boron, 
potassium, sodium, lithium, barium, calcium, magnesium, aluminium, 
manganese, and iron. These, combined in various ways, compose 
the greater part of the earth's crust, and of its liquid envelope. By 
remembering or consulting the table of the atomic weights we have 
the proportion in which they combine among themselves, and also 
their atomicity, or power of replacing, sometimes called substitution 
by equivalents. These two facts are of great importance. 

All rocks are composed of minerals, sometimes of one, when it is 
called a simple mineral, as limestone, consisting mainly of calcite ; 
or it may be made up of two or more, as granite, being then called 
a compound mineral. With the exception of the following minerals, 
which are either elements or binary compounds— namely, carbon, 
quartz, rock salt, fluor-spar, iron pyrites, and hasma.tite — the other 
rock-forming minerals are chiefly silicates, carbonates, or sulphates, 
the silicates being by far the most abundant, the carbonates next, 
and then the sulphates. There are nearly in every case accessory 
ingredients as well as the essential ones. The principal minerals 
are quartz, felspar, mica, hornblende, augite, clay, calcspar, and 
dolomite. 



PHYSIOGRAPHY. 31 

44. Decomposition of Compounds.— The general method of 
decomposing compounds is by means of chemical affinity. Thus, 
suppose we have a compound, AB, which we wish to resolve into its 
elements, A and B, we must add to the compound a substance, C, 
which we know has a greater affinity for one of the elements than 
the other element in the compound has — that is, C miv/c have a 
greater affinity for A than B has, the result of which is that A and 
C combine, leaving B at liberty. Again, if we wish to libeitite A, 
we must mix with the compound AB a substance, D, which has a 
greater affinity for B than A has. Then B and D combine, leaving 
A at liberty. The chief agent in decomposing rocks is carbonic acid 
gas, as water charged with this gas dissolves the majority of them. 
For example we will take granite. 

Granite is composed of three minerals — quartz, felspar, and mica. 
Of these quartz is insoluble; but the acid will readily attack the 
felspar, which consists of sihcate of alumina and silicate of potash, 
soda, or other alkali. The acid having a greater affinity for the 
alkali (potash, soda, &c.) of the silicate than silicic acid, forms with 
that alkali a carbonate which is soluble in water. The sihcate of 
alumina, being unaffected by the acid, is set free as an insoluble 
clay [Kaoliri], this decomposition yielding carbonate of potash or of 
some other alkali, according to the chemical composition of the silica 
and felspar, which are dissolved in the water, and clay. It is in 
this way that rocks get broken up by natural causes, carbonic acid 
existing largely in the atmosphere, in most waters (which is the 
next chief agent in breaking up rocks, &c.), and combined with 
minerals in a solid state, as in marble, which consists of lime united 
to carbonic acid. It is easy to understand that any one constituent 
of a substance being decomposed, the other constituents will be 
freed and readily removed by running water. 

Gneiss may also be broken up into the same substances as granite — 
namely, felspar, mica, and quartz — but the minerals are arranged in 
more or less thin layers. Fine examples of this rock occur in the Alps. 

Syenite, another rock of this kind, may be broken up into felspar, 
hornblende, and quartz. Protogine is composed of felspar, talc, and 
quartz. Mica-schist consists of alternate layers of quartz and mica, 
the latter of which mostly preponderates. Talc-schist, is composed 
of layers of quartz and talc. Trachyte, composed of sanidine felspar, 
and a Uttle mica or hornblende. Basalt, containing basic felspar, 
titanio-ferrite, augite, and generally olivine. Felsfone, composed of 
acidic felspar and quartz. Melaphyre, composed of basic felspar, 
magnetite, augite, and generally chlorite. Diabase is similar to 
melaphyre. Greenstone or diorite consists of hornblende and felspar. 
Dolorite consists of augite and felspar. 

It will be seen that felspa/r and quartz are contained in most of 



32 



PHYSIOGEAPHT. 



the principal rocks, common quartz being the most abundant of all 
minerals. We will now give the chemical composition of a few of 
the chief minerals. 

Quartz is formed from pure silica (SiOg). 

Fdspar, a silicate of alumina and potash (AI2O3, SSiOo+KO, 
SSiOa), giving a percentage of silica 65'35, alumina 18'0"6, and 
potash 16'59. A little soda always occurs. 

Mica (potash) is a silicate of potash and alumina (KO, SSiOg + 
AlgOg, SiOg). A part of the potash may be replaced by lime and 
the protoxides of iron and manganese, and part of the alumina by 
the corresponding oxides of iron, manganese, and chromium. One 
analysis gives siHca 47, alumina 20, potash 14:"5, oxides of iron 15*5, 
oxide of manganese 1'75 per cent. 

Mica (lithia), or Lepidolite, is a silicate of alumina, potash, and 
lithia, in combination with a fluoride. 

Hornblende is essentially a silicate of magnesia, mixed with silicates 
of lime, iron, &c., the chemical composition of which varies much. 

The minerals of the Talc group are hydrous silicates of magnesia 
and alumina. 

Tracliyte often contains disseminated crystals of glassy felspar, 
hornblende, a little quartz, and mica. Composition — Silica 6 7 '09, 
alumina 15-64, potash 3*47, soda 5'08, lime 2*25, oxides of iron 4'59, 
magnesia '98, oxide of manganese "15, water, &c,, *83. 

Cliiikstone or Phonolite is composed of silica 56 "28, alumina 20 '55, 
potash 5-84, soda 9-07, oxides of iron and manganese 4'31, titanic 
acid 1*44, magnesia '32, lithia "05, &c. 

Clay consists chiefly of silica and alumina, but is sometimes mixed 
with lime, magnesia, &c. 

TABLE OF THE MOST ABUNDANT SIMPLE MINERALS. 
PERCENTAGE ANALYSIS OP ROCK-FORMING MINERALS. 







ci 

1 

< 


j 


S 


1 


i 

m 






s 


1 

1" 




Quartz (when piire) . . 
U Albite ..".WW 


100 
65-35 

70-48 

63-50 

53-70 

45-5 

47 

50-35 

56-36 

47 

62-80 

30-40 

56-50 

42-30 


18-06 

18-45 

23-10 

29-67 

34-5 

20 

28-30 

12" 

1 
7 


•80 

is'-is 

13 

32-40 

34 

21 

44-20 


•55 
2-40 
12-13 
17 

25-46 
14 

14-5 


16-59 
2*20 

14*50 
9-04 


10*50 
9-40 

4-50 


1" 
15-50 

14* 
1-60 
4-40 
6 
•20 


1-75 
1-23 


5*49 


1' 

:: 

2-30 
12-60 

2 
13-30 


2-6 
2-5 


g"- OUgoclase 

^ Labradorite .... 

^ VAnorthite 

Mica (Potash Mica).. 

Mica (Lepidolite) 

Augite 


2-6 
2-6 
2-7 
2-9 
2-9 
3-3 


Hornblende . , 

Talc 


. 




3-2 

2-e 


Chlorite 


9:1 


Antinolite 


S 


Serpentine 


2-8 



PHYSIOGRAPHY. 33 

From the preceding table it will be seen tbat the cbief con- 
stituents of the rocks, &c., are silica, alumina, magnesia, oxide of 
iron, Hme, potash, soda, carbonic acid, and water ; and reducing 
these still further to their elements we find that silica is a 
compound formed by the union of silicon with oxygen ; alumina. 
by the union of aluminium with oxygen. Magnesia occurs in 
two states, sometimes as carbonate, in certain Hmestones, and 
sometimes as sulphate ; hence it is composed of either carbon 
and magnesium or sulphur and magnesium. Oxide of iron is 
oxygen and iron combined ; lime is oxygen and calcium ; potash, 
oxygen and potassium; soda is obtained from a compound of 
chlorine and sodium ; carbonic acid is carbon and oxygen combined ; 
water, hydrogen and oxygen. From the above description we see 
that the elements which enter largely into the composition of rocks 
are very few, namely, oxygen, silicon, aluminium, calcium, magnesium, 
iron, carbon, sulphur, chlorine, and sodium, being in the order of 
their relative abundance, oxygen being the most abundant of all 
known substances, constituting at least one-third of the solid mass 
of the globe, eight-ninths of the water, and nearly one fourth part 
of the atmosphere ; it also exists in most organic substances. 
Taking into account the composition of the water of the earth and 
its atmosphere, the two gases, hydrogen and nitrogen, are also of 
primary importance, the former forming one-ninth of all waters, and 
the latter four-fifths of the atmosphere. 

WATER: ITS COMPOSITION AND SEVERAL 

STATES. 

45. Water is composed of two volumes of hydrogen and one ot 
oxygen ; or,^ by weight, one part hydrogen to eight parts oxygen, 
namely, ll'll per cent hydrogen and 88-88 per cent oxygen. It is the 
most important ("element," as the ancients called it) compound in 
the constitution of the globe, being, we might nearly say, everywhere. 
It always exists in the air in an invisible state, giving the blue 
appearance to the sky, and becomes visible in the form of clouds. 
It forms a constituent of all animal and vegetable substances, and 
also of the rocks and minerals which compose the crust of the earth. 
When pure and at ordinary temperature it is a fluid without taste 
or smell. In large bodies, as in seas and oceans, it has a peculiar 
bluish-green colour, but in small quantities appears colourless. 
When heated, under the ordinary pressure of the atmosphere, to the 
temperature of 212° F., at the level of the sea, water boils and is 
converted into steam. The higher we ascend the pressure of the 
atmosphere becomes less, water thereby boiling much sooner. Thus 
on the top of Mont Blanc, which is about 15,000 feet above the level 
of the sea, water was found to boil at 178° F., or 34° below ita 
C 



34 PHYSIOGRAPHY. 

usual boiling temperature. What would be cooked at tbe sea-level 
might remain unchanged for hours in the boiling water at the 
summit of the mountain. 

There is one point regarding water, in its diflferent states and 
temperature, worthy of particular notice, and that is, its expansion 
and contraction follow a different law to all other bodies, with the 
exception of bismuth, which expand in proportion as they are 
heated and contract in proportion as they are cooled. If water be 
heated to its boiling point it will expand like other liquids, and if 
allowed to cool it will follow the general law, viz., contract, until it 
attains a temperature a little below 40° F,, at which point it attains 
its maximum density, that is its minimum or least volume. If 
the water still continues to diminish in temperature it will now 
begin to expand until reaching the freezing point, or 32° F., and if 
cooled below this point, by being kept perfectly still, it will continue 
to expand, and in the act of freezing a sudden and considerable 
expansion takes place. Its effect may be noticed on water-pipes, &c. 

If water followed the general law, and continuously contracted on 
cooling, it is evident that its weight, bulk for bulk, would get heavier 
and heavier ; hence, as soon as the surface of our rivers was frozen 
and ice formed on the top it would sink to the bottom ; then the 
fresh surface would in its turn freeze and another layer of ice sink ; 
and this would go on, even if the winter was not severe, until our 
rivers, ponds, and lakes, were converted into solid masses of ice, 
thereby causing destruction to their inhabitants. But such is not 
the case. It has been ordained by the Creator, in His infinite 
wisdom, that the water should expand, instead of contracting, below 
40° F,, thereby becoming lighter than the warmer water underneath, 
causing it to float on the surface instead of sinking, and helping to 
form a covering or protection to the water below and its inhabitants. 

Water, as found on the earth, is seldom or ever absolutely pure, 
but contains more or less of various substances. Even rain water, the 
purest of all, contains small quantities of impurity, and that of rivers 
and springs much more. The water running through the ground 
dissolves more or less of the substances it meets with, and these sub- , 
stances sometimes become so abundantly taken up that the water 
acquires a strong taste and active medical properties. Such is the 
cause of the mineral springs so-called. Among the various substances 
found in water the chief are silica, alumina, salts of lime, mag- 
nesia, soda, potash, iron, manganese, atmospheric air, carbonic acid, 
nitrogen, &c. ; in the sea are also found iodine and bromine. 

Water may be either in a liquid, solid, or gaseous state. As water 
inits fluid state, rain, dew ; solid state, ice, snow, hail ; gaseous state, 
vapour, steam. These different states are all caused by different 
degrees of heat. (See " Cohesion," page 15 ; and for formation of 
rain, dew, snow, hail, &c., see page 117.) 



PHYSIOGRAPHY. 35 

Latent and Specific Heat of Water. — Water, like all other sub- 
stances, has what is termed latent (hidden) heat ; that is, heat ^vhich is 
not perceptible to our feelings. Thus, the temperature of ice is 32° ; 
but if 144° of heat be communicated to it it will feel no hotter, but 
simply cause it to become a liquid, the 144° of heat being hidden in a 
latent condition in the ice. In ice there is altogether 1,116° of latent 
heat, 972° of heat being secreted when water is converted into steam. 

The specific heat or capacity for heat of a body is the quantity of 
heat necessary to raise it through a certain number of degrees as 
compared with the quantity required to raise an equal weight of 
water through the same number of degrees. Of all substances water 
possesses the greatest capacity for heat ; hence, when cooled through 
a certain range of temperature it parts with the greatest amount of 
heat. The high specific heat of water plays an important part in 
the economy of nature, the specific heat of water being 1, and 
of the air -2374, or nearly 4-2 times less than that of water; there- 
•fore 1 unit of water in losing 1° would warm 4 '2 units of air 1° ; but 
water is also 770 times as heavy as air, so that, comparing equal 
volumes, a cubic foot of water in losing 1° would raise 4*2 x 770, or 
3,234 cubic feet of air, 1°. We see from this the great influence 
which the ocean must exert on the climate of a country. The heat 
of summer is stored up in the ocean and slowly given out during the 
winter. Hence one cause of the absence of extremes in an island 
cHmate.* 



GEOLOGY. 



EELATING TO THE EARTH'S CRUST. 

46. The Crust of the Earth. — By the crust of the earth we are 
to understand the solid exterior as far as it is known to us by 
observation and inference. It is supposed that the earth was once 
in a state of fusion, and that having cooled by radiation, the outside 
cooling more than the interior caused a solid superficial layer ta 
be formed. This consists of a variety of solid materials, to which 
the general term roch is given, which term includes not only stony 
and compact rocks like granite, limestone, &c., but soft and loose 
matter, as sand, clay, and gravel. The chemical character and com- 
position of the chief of the rocks are given on page 32. We will 
now consider the physical character and features of the chief of them. 
The greater part of the rocks at the surface of the earth occur in 

* Tyndall on "Heat as a Mode of Motion," page 143. 



36 PHYSIOGRAPHY. 

regular beds — each bed maintaining an almost uniform tluckness — 
appearing like piles of cloth piled upon each other. This class of 
rock is called stratified; but also denominated aqueous rocks, on 
account of being deposited from water when for the time the 
(Substances of which they are composed were either chemically or 
mechanically suspended ; and sedimentary, because they are tho 
accumulations of sediment carried in the sea by rivers. There is 
another class of rocks termed unstratified, igneous, or plutonic, being 
called unstratified because no traces of layers or beds can be- 
detected, the rock forming merely a great mass of mineral matter ; 
and igneous, or plutonic, because they have evidently been in a 
melted state through the action of very great heat. 



SEDIMENTARY, OR AQUEOUS ROCKS. 

47. The Aqueous Rocks may be divided into three classes, 
according to their mode of origin : (1) Mechanically-formed rocks — 
those formed mechanically from the ruins of existing rocks, such 
as conglomerate, sand, clay, shale, &c. (2) Organically -formed 
rocks — those consisting of accumulations of vegetable or animal 
remains, such as coal, peat, &c. (3) Chemically -formed rocks — those 
resulting from chemical means, as rock salt, gypsum, &c. They may 
also be divided into three classes, according to their composition, 
namely, as arenaceous, or sandy ; calcareous, or hmestone ; and 
argillaceous, or clayey rocks. 

(1) Mechanically -formed Rocks are merely fragments of 
rocks broken up by the action of frost, snow, rain, rivers, &c., and 
again deposited as sedimentary strata. 

Arenaceous. — In this division we have shingle, gravel, con- 
glomerate, hreccia, sandstone, and grit. Shingle consists of pebbles 
of rock, not cemented together in any way, being rounded by the 
action of the stream or river, having their sharp angles and edges 
worn off. When the pebbles are smaller and mixed with sand it is 
called gravel, and sand when the fragments are very small. Con- 
glomerate, or pudding-stone, is a rock consisting of rounded pebbles 
cemented together, the cementing material filling the interstices 
and rendering the whole a hard compact rock. If the materials are 
angular it is termed a hreccia. The pebbles may consist of any sub- 
stance whatever, and the conglomerate is named, according to tho 
constituents, silicious, or quartzose-, granitic, calcareous, &c., though 
mostly consisting of quartz, or some very sihcious mineral, owing 
chiefly to the greater abundance of the silicious over other mineral 
matters that enter into the composition of the rocks. When the term 
conglomerate is used alone it is always understood to mean a rock 



PHTSIOGBAPHT, 37 

composed of quartz pebbles. The cementing material may be either 
iron (ferruginous), sand (arenaceous), lime (calcareous), or clay 
(argillaceous). Sandstone is fine sand consolidated, but if the par- 
ticles are coarse it is called grit or gritstone. 

Abgillaceous, OB Clayey. — The most simple class of this rock is 
day, which results from the decomposition of felspathic rocks, &c., 
by the agency of acid waters. It is mostly found in an impure state, 
mixed with fine sand, flakes of mica, organic remains, &c. When 
pure it is found to be a hydrated silicate of alumina, being found 
pure only in the case of kaolin. The clayey materials, by subsequent 
changes, become solid rocks; thus, the agency of pressure alone 
having successively formed shale, slaty-shale, and clay-slate, each of 
which varies in texture and composition. There are a great many 
different varieties of clay, each receiving special names. Pipe-clay, 
so called from its being used in the maniifacture of tobacco pipes, 
is white and almost pure. It is sometimes termed potters' clay. 
Fire-clay contains very little iron, lime, or alkalies. It contains 
much silica, and often carbon ; still being able to stand great heat 
without melting. Bituminous-clay contains bitumen. Others, con- 
taining oxides of iron, by which they are variously coloured, are 
termed variegated. 

Shale is a laminated clay rock, which will split into thin plates 
along the original planes of deposition. When very hard, splitting 
into fine slabs, it is called slate, or clay-slate. A very large propor- 
tion of the strata comprising the coal measures is constituted by this 
rock.' 

Marl is a calcareous clay, being composed of clay and carbonate 
of lime or carbonate of magnesia. It effervesces with an acid, and 
breaks when dry into small cubical or rounded fragments. When 
the rock contains less than one-half of clay it ceases to be marl, 
being then called an argillaceous hmestone. There are many kinds 
of marl. When it contains much carbonate of lime it is said to be a 
calcareous marl ; if it contains dolomite, with carbonate of Hme, 
a dolomitic marl ; or with a minimum percentage of calcareous 
matter, an argillaceous marl ; arenaceous, with much sand ; micaceous, 
with mica ; shell marl, found at the bottom of old ponds, ditches, 
or lakes, formed from the decomposition of shells, &c. 

Loam is a mixture of clay and sand, not so plastic as clay, and 
permeable by water. 

Mud and silt are the materials of some form of argillaceous rock 
not cemented together, either clay, shale, loam, or marl, as the case 
may be ; resulting from the waste of these rocks by running water 
and other natural agents of decomposition. The accumulations are 
formed by the particles, which are very small, being carried by 
running water, and deposited where the water is quieter, as at the 
mouths of rivers, &c. 



S8 PHYSIOGRAPHY. 

Composition op Sueface Soil. — Soil adapted to the growth of 
plants consists of two principal portions — the organic and the 
inorganic. The former, or humus, consists of decayed remains of 
animal and vegetable matter, but varies much in different sois. 
For instance, peaty soils contain from one-half to three-fourths of 
their whole weight of this matter ; but generally soils do not contain 
more than from 3 to 8 per cent, though stiff clayey soils, containing 
from 10 to 12 per cent, have been noticed. The inorganic portion of 
the soil consists of two minor divisions — the soluble saline portion, 
from which saline ingredients are obtained, and the insoluble caHhy 
portion, which constitutes the great bulk of most soils, being seldom 
less than six-sevenths of the whole weight, the remaining seventh 
consisting of organic matter and soluble saline, in about equal 
portions. 

The constituents of this insoluble earthy portion, or the greater 
part of all soils, are silica, alumina, and lime. The first appearing 
in the form of sand ; the second (alumina), mixed with sand, aa 
clay ; and lime, in the form of carbonate, as limestone, chalk, &c. 
According to Johnson, dry ordinary soil, containing one-tenth of 
clay, forms a sandy soil ; if it contains from one to four tenths it 
is a sandy loam; from four to seven tenths, a loamy soil; from 70 
to 85 per cent, a clay loam; from 85 to 95 per cent, a strong clay, 
fit for brickmaking ; if it contains no sand, it would be a pure 
agricultural clay, or pipe-clay. 

Very few arable lands contain more than from 30 to 35 per cent 
of alumina. Soils are called mao-l if they contain more than 5 per 
cent of carbonate of lime, and calcareous or chalky when more than 
20 per cent — the soil appearing whitish, as on the south-east coast 
of England. 

The soluble saline portion is made up chiefly of common salt 
(chloride of sodium) , gypsum (sulphate of lime), glaubers and epsom 
salts (sulphate of soda and of magnesia), with shght traces of 
the chlorides of calcium, magnesia, and potassium, the nitrates of 
potash, lime, soda, <fcc. 

(2) Organically-formed E.OCks form a very important class, 
on account of their extent and thickness, and also their value, as in 
the case of coal, limestones, &c. 

Limestones are of various kinds, being of various formations. 
Among the most important are the following : Chalk, Metamorphic 
Limestone, Dolomitic or Magnesian, Oolite, Hydraulic, Siliceous, 
Mountain Limestone, &c. Nearly all are formed by the elimination 
of the lime from the ocean by the agency of organic life, the shells 
having been ground to a powder by the action of the sea, and 
afterwards cemented together. Limestones are generally composed 
of calcite, that is, calcium and oxygen ; but impuiities, as silica. 



PHYSIOGRAPHT. 39 

oxides of iron, clay, or carbon, are often mixed with it. Thus, the 
common limestone consists of two binary compounds ; calcium and 
oxygen, forming calcite, and carbon ajad oxygen, forming carbonic 
acid. If the stone is burned the carbonic acid is expelled, and pure, 
or quicklime is obtained. Limestones present every variety of hardness 
and texture, from the soft chalh to the hard crystalline marble. 

Chalk is a white earthy limestone, being made up of the minute 
shells of Foraminifera. It is one of the most pure, containing about 
44 parts carbonic acid and 56 parts lime. It is very useful as a 
manure in improving the texture of the soil Magnesian limestOTie 
consists of carbonates of hme and magnesia. Many of these stones 
appear to have been formed from limestones of true organic origin 
by the action of solutions containing magnesia. The Dolomite 
contains about 30 parts Hme, 21 magnesia, and 49 carbonic acid. 
The others do not contain so much carbonate of magnesia, varying 
from that in the dolomite down to only a few per cent. 

Hydraulic limestone contains some clay and silica, and affords a 
lime the mortar of which will set hard under water. 

Oolitic limestone consists of minute spherical concretions, appearing 
like the roe of a fish— hence the name. It is mostly of a grey, 
greyish white, or yellowish colour, and, being easily worked, is largely 
used as a building stone ; examples of which are Bath, Portland, and 
Caen stone. In the case of Portland stone, there is upwards of 96 
per cent carbonate of Hme, a trifle more than 1 per cent of carbonate 
of magnesia, and about 1 per cent of siHca, a little oxide of iron, &c. 
Coral, or Mountain Limestone. — The coral reefs are built by what 
we may term an endless number of tiny animals called polyps, which 
take the Hme from the sea, building these reefs and islands from 
the bottom of it, forming very large deposits of limestone. It is 
probable that their works are eternally going on : new islands con- 
tinually emerging from the depths of the ocean. Coral consists of 
carbonate of calcium, with variable quantities of other salts of cal- 
cium and magnesium, and some organic matter. The red colour in 
some descriptions is said to be of organic and not mechanical origin. 
Siliceous limestone contains silica, diffused through the limestone, 
and is harder than ordinary Hmestone. On decomposition of the 
calcareous matter it leaves the siliceous residuum, forming rotten- 
stone, so much used in brightening metals. 

Flint is found in layers of nodules in chalk, a mixture of sHica and 
Hme. It is supposed to owe its origin partly to the presence of 
siHceous organisms. Chert is a similar rock. 

Carbonaceous Geoup. — In this group we include those which 
afford coal and resin, being chiefly products of vegetable accumula- 
tions, and mostly combustible. The most important is coal, of which 
there are many descriptions, varying greatly in composition, hardness, 
and texture. Some chemists have separated the elements of coal into 



I 



40 PHYSIOGKAPHT. 

volatile matter, charcoal, and ashes ; others into carbon, oxygen, and 
hydrogen ; others into charcoal, bitumen, and earth, according to the 
method of analysis. The chief varieties are as follows : — 

Anthracite consists chiefly of carbon containing very little bitu- 
minous matter. It is hard, lustrous, and has the shining appearance 
of black lead. It does not soil the hand and emits little or no flame, 
but intense heat. Its specific gravity is about I"4. It contains 
about 90 per cent of carbon, 3 per cent of hydrogen, the remaining 

7 per cent consisting of oxygen, nitrogen, &c. 

Bovoy coal, or Lignite (so-called from being foand at Bovey, in 
Devonshire), is a kind of wood-coal (lignite), existing chiefly in the 
rocks of tertiary formation. It is of a dark-brown colour, and 
consists of wood permeated with bitumen, and often contains 
pyrites, alum, &c. This coal often shows the original woody fibre 
very little altered in appearance. When fiisb dug out of the earth 
it is soft in consistence, but becomes harder rapidly on exposure. 
Its constituent parts are found to consist of 77*1 of carbon, 19'35 of 
oxygen, 2*54 of hydrogen, and 1 of earthy substance. 

Cannel coal varies very much in appearance. It burns with a 
bright clear flame, like a candle (hence its name), and is a valuable 
coal for the making of gas. It does not soil the fingers when it is the 
glossy kind. Its constituent parts are 66 of carbon, 11 of oxygen, 

8 of hydrogen, 1 of nitrogen, and 1 of earthy substance. 

Pit coal is the ordinary coal of household use. It varies much 
in appearance and quality, some kinds caking when burnt, owing to 
the quantity of bitumen, or mineral pitch, which it contains, 

Bitumous coal contains bitumous matter, more or less, varying 
from one-tenth to three-fifths of the whole. It burns with a bright 
flame, and is softer and not so bright as anthracite. 

Splint coal is a very hard variety, obtained in large blocks. It is 
used chiefly for steam and furnaces. It contains about 80 per cent 
of carbon, 8 of oxygen, 6 of hydrogen, 1 of nitrogen, and 5 of earthy 
substance. 

Coal is the product of the fossilisation of ancient vegetation, 
either on the places where it grew, or on those into which it had been 
drifted. By taking a thin slice of coal and examining it under a 
microscope, traces of vegetable tissues can in most cases be made out, 
especially indications of spore cases of club mosses and other flower- 
less (cryptogamic) plants. There may be noticed fern leaves, stems, 
barks, &c. Other facts going towards proving the vegetable origin 
of coal is its chemical composition, which is the same as wood, 
namely, carbon, hydrogen, and oxygen, together with some earthy 
substance which forms the ash in each case. 

Peat or Turf is, like coal, of vegetable origin. It is formed chiefly 
from mosses in bogs and swamps, in which shrubs and trees often 
get buried. When vegetable matter is exposed to moisture and 
excluded from air chemical changes take place, the result of which 



PHYSIOGBAPHT. 41 

is, the vegetable matter loses carbonic acid and water, becoming 
changed into x>^at or imperfect coal ; losing more carbonic acid and 
water it becomes lignite or wood coal ; still losing the same acid and 
water, in addition to a compound of carbon and hydrogen called 
marsh gas — which is the fire-damp met with by the miners — the 
lignite becomes coal ; further losing more carbon and hydi'ogen it is 
converted into the hard glossy anthracite. In some layers of peat the 
actual species of moss may yet be determined. The growth appears 
to be still going on rapidly in some places, as, according to Leonhard, 
in Alt-Warmbriicher Moor, near Hanover, the turf or peat has been 
re-formed in fifty years, and during the last thirty years a layer from 
four to six feet thick has been in course of formation. The chief 
formations of this kind are the great bogs of Ireland, in which the 
roots, trunks, and branches of large trees, both pine and oak, are 
abundant ; iron pyrites are also in abundance, very often causing 
spontaneous combustion and the formation of sulphates. Turf is 
also found in the tropics, as, for in&tance, at San-Panco, in the Brazils ; 
and on the banks of the North Sea a species is formed from the 
accumulation of seaweed. 

(3) Chemically-formed Rocks (Calcareous).— The greater 

number of the chemically-formed rocks are composed of carbonate of 
lime. Through the integrating power of water containing carbonic 
acid gas flowing through limestone rocks, some of the stone is dis- 
solved, and when a portion of the gas escapes from the water the 
dissolved limestone is again deposited, mostly in beautiful crystals, 
called stalactites* that hang from the roofs and sides of caverns. 
The water slowly percolating through the rock, or calcareous bed 
dissolves its substance in its progress and appears as a drop upon 
the roof of the cavern, where it is suspended for a moment or so, 
diuing which time it loses carbonic acid gas and deposits carbonate 
of lime. The drop then falls to the floor of the cavern, carrying 
some portion of the dissolved limestone. The continuation of theso 
drops form, on the floor of the cavern, either as a pinnacle, termed a 
stalagmite, -{^ or as a stalagmitic sheet covering the floor of the 
cavern. 

In districts where there is much limestone, the cold springs as they 
emerge from the rocks are often so highly charged with carbonate of 
Kme that on reaching the open air they yield calctufi", or sinter, in 
the form of calcspar ; and hot springs that of aragonite. Calctuff 
is usually a porous friable deposit, but sometimes its layers are firm 
enough to be used for buildmg purposes, being very valuable from 
their lightness. Travertine is a similar rock, but usually more 
compact. A mass 30 feet thick has been formed in twenty years at 

* Gr. Stalasso, to drop. f Gr. Stalagma, a drop. 



42 PHYSIOGRAPHY. 

the baths of San Fillippo. These springs have received the popular 
name of petrifying springs, on account of their giving a stony 
appearance to wood, moss, and other objects placed in them for 
some time, but it must be remembered that the object itself is 
unchanged, the carbonate of lime being deposited in a firm and 
solid state on them. 

Gypsum is a chemical deposit composed of sulphate of lime. 
Some deposits owe their origin to the result of the evaporation of 
sea water, while others are supposed to be produced from the local 
conversion of limestones, by the agency of gases, or by infiltration. 
It sometimes occurs in beds, as in the neighbourhood of Paris — 
hence the name plaster of Paris, viz., ground gypsum — but mostly 
as irregular masses, intercalated in marls, appealing as veins or 
strings. It is also of frequent occurrence, as isolated crystals, or 
aggregates of crystals, in most clays, being then called alabaster. 

Jtock salt is also a chemical deposit, similar in origin to gypsum, 
namely, resulting from the evaporation of sea water, but especially 
of salt lakes, when there is no outlet (the evaporation being equal to 
the supply). The water though completely saturated with salt is 
continually receiving more ; hence there must be a continual deposi- 
tion of salt going on at the bottom. This rock is one of the few 
binary compounds, being composed of chloride of sodium. It occurs 
in large wedge-shaped masses in some localities, and sometimes in 
immense beds, as in Cheshire, and at Wicliczka, in Poland, and is 
always accompanied by gypsum. 

Sulphur is found in a calcareous marl in Italy, varying in thick- 
ness from 4 to 31 feet. 



METAMORPHIC EOCKS. 

48. The Metamorphic Rocks are a group of rocks that were 
originally sedimentary or stratified, but have undergone a change of 
structure, or metamorphosis, by heat or pressure, the chemical com- 
position remaining the same, but grouped together in different ways. 
This metamorphism does not always destroy the original character, 
but simply hardens the rock, as, for instance, sandstones hardened 
into hard rocks, called quartzite, limestones into marbles, clays into 
slates, &c. ; but in some cases it does destroy the original character, 
rearranging the elementary substances of sedimentary rocks, con- 
verting them into rocks having a mineral composition similar to the 
igne >us rocks from which they had originally been derived by 
chemical agencies, as, for instance, sandstones and clays may be 
converted into rocks whose composition is similar to granite, namely, 
quartz, felspar, and mica, and so on ; but they may be generally 
distinguished, as they still retain more or less of their original 



PHTSIOGBAPHT, 43 

stratification, and tlie minerals have a tendency to arrange themselves 
in layers, splitting easily along those planes, thereby differing from 
igneous rocks, which display neither of these features. 

The chief metamorphic rocks are quartzite, mica-schist, gneiss, 
granite, crystalline, limestone, serpentine, &c. 

Q,uartz rock, or quartzite, is a compact and granular rock, consisting 
of nearly pure quartz. It is not far removed from ordinary sand- 
stone, the half -fused state of its component grains showing at once 
that it is a sandstone which has been altered by the action of heat, 
or of heat and water. 

Gneiss consists of felspar, mica, and quartz, the felspar lamellar 
and the mica being arranged in lines, producing a foliated or schistose 
structure. This rock varies much in appearance. Sometimes the 
Lamince preserve their parallelism for great distances ; but in other 
cases it is so obliterated that it cannot be determined from granite. 

Mica-schist consists of alternate layers of mica and quartz, the 
mica preponderating. It readily splits into thin scales or lamince, 
some varieties affording good roofing slates, such as hornblende-schist, 
consisting of hornblende and quartz. Chlorite-schist is a green slaty 
rock, in which chlorite is abundant, usually blended with quartz, 
though sometimes with felspar and mica. 

Serpentine is a compact amorphous rock, consisting chiefly of 
silicate of magnesia. It is usually of a green colom*, but sometimes 
variegated, resembHng the skin of a serpent. 

Granite, as before stated, is a rock composed of quartz, felspar, 
and mica. It is easily distinguished from other rocks by its mottled 
appearance. There seems to be a diversity of opinion whether this 
rock is of igneous origin, or simply the result of the extreme of 
metamorphism, though it is certain that many granites are true 
igneous rocks. 

IGNEOUS OR UNSTRATIFIED ROCKS. 

49. Igneous Rocks are all those which do not come under the 
definition of aqueous or metamorphic, showing traces of once having 
been in a state of fusion, or molten by heat (" igneous " meaning: fixe). 
They are mostly divided intp two classes, viz., volcanic and plutonic 

Volcanic Rocks are those which have been ejected in a melted 
state from volcanoes or fissures in the earth's crust, as lavas and 
ashes, which are good examples of igneous rocks — lava especially, as 
we can see it issue from the crater of a volcano as a molten stream, 
being afterwards turned into a hard rock. These volcanic rocks are 
divided into two sections — the felspathic or trachytes, having light 
colours and being of low specific gravity, containing an excess of 
silica, but poor in earthy bases and the oxides of iron ; and tha 



44 PHYSIOGRAPHY. 

augitic or basaltic, having dark colours with high specific gravity, 
containing a large percentage of earthy bases and the oxides of iron, 
but poor in silica. 

(1) Felspathic or Trachyte rocks are generally crystalline granular 
compounds. They are called trachyte on account of their rough 
texture, and are chiefly composed of acidic felspar, the specific 
gravity varying from 2*4 to 2"8. The grandest examples of these 
rocks are in Central and South America, in the chain of the Andes, 
of which they form the summits, the beds being sometimes from 
14,000 to 18,000 feet thick, as oJBf Chimborazo and the volcano 
Guangua-Pichincha. 

Trachyte is usually of a greyish colour, and of a rough texture. 
It is composed of sanidiue felspar, and mostly a little mica, or 
hornblende. When distinct crystals of felspar exist the rock is 
called trachyte porphyry. There are many varieties, such as domite, 
earthy and friable ; hornblende trachyte, containing much hornblende 
in disseminated crystals ; slaty trachyte, &c. 

Pumicestone is very light, usually of a light colour, and containing 
about 70 per cent of silica. It has minute capillary and parallel 
pores, these pores being due to the escape of gases. 

Obsidian is a volcanic glass, similar to coarse bottle glass, varying 
in colour from brown to greenish-black and black. 

Clinkstone or Phonolyte, so called from its ringing sound when 
struck, is of variable composition, but is chiefly composed of glassy 
felspar with a zeoHte in variable proportions. It is of a greyish blue 
and other shades of colour, generally splitting into thin slabs and 
containing zeolite disseminated through it. 

Pearlstone is something similar to pitchstone, but not so glassy 
and more pearly. It is mostly of a greyish colour. 

(2) Augite or Basaltic Rocks. — These rocks contain a great quantity 
of augite,* which prevails over the felspar, rendering them augitic 
rather than felspathic. They are of high specific gravity — namely, 
from 2*9 to 3*7 — and range in colour from dark grey to black, the 
dark colour and high specific gravity being due to the presence of 
iron. The composition of these basalts include titano-f errite (titanic 
acid and iron) and ohvine (a silicate of magnesia and iron), as well as 
augite and felspar. The most important varieties are as follows : — 

Basalt is a compact, and nearly or altogether a black rock, and 
usually composed of basic felspar, augite, titano-ferrite, &c. This 
rock often occurs in columns more or less hexagonal in section, 
examples of which are the basaltic rocks in Fingal's Cave and the 
Giant's Causeway. 

Bolerite (deceptive) consists of labradorite and augite, with some 
magnetic iron. It has a crystalline and granular texture, and is of a 

* A green mineral, composed of silicate of lime with, magnesia and iron. 



PHYSIOGRAPHY. 45 

black or greenish-black colour. Specific gravity, from 2 "8 5 to 3'1. 
The variety anamesite is a similar rock but finer grained, being 
intermediate in texture between basalt and dolerite. 

Levxitophyr, or leucite rock, of a dark grey colour, fine grained, 
tellular, consisting of augite and leucite, &c. 

Ashes are merely fragments of the foregoing rocks which have 
been reduced to various degrees of fineness. When they appear as 
cinders they are called scm-ice ; when the lava, in its journey 
through the air, takes of a spherical form more or less, they are 
bombs; when cemented together in beds or masses, tuff; or as 
small stones, or fragments of ejected rock, lapilli, &c. 

50. Plutonic Rocks are supposed to be of igneous or aqueo- 
igneous origin, formed under great pressure — having been melted 
and afterwards cooled and crystallised, but very slowly, in the 
depths of the earth. They consist of crystallised silicates, with 
or without free quartz, and other minerals — such as iron pyrites, 
&c. — ^in smaller quantities. The chief of this group is granite, 

(1) The ordinary kind consists of orthoclase quartz and white 
mica, disseminated in nearly equal proportions. The felspar is 
lamellar and the texture mostly granular, sometimes being finely 
grained and at other times coarsely grained. Its colour is either 
greyish or reddish, depending chiefly on the colour of the felspar. 
There are several kinds of granite, some of which are — Syenite^ 
which is a hornblende granite, consisting of a felspar, quartz, and 
hornblende, the felspar lamellar often predominating. Pegmatic 
consists of lamellar orthoclase felspar and quartz, often arranged 
in broken lines. Eurite, being blended into a finer granular mass, 
though of same constitution as granite. Protogine (first produced) 
is of the same composition, with the exception of talc in the place of 
mica. Granite and granitic rocks are abundant in some parts of the 
British Isles, constituting the greater part of the Grampians in 
Scotland, and the mountains of Cumberland, Devon, and Cornwall, 
also the Wicklow Mountains, in Ireland, &c. 

(2) Those generally classed as trap-rocks — from the Swedish 
trappa, a stair — these rocks being supposed usually to assume a 
step-like form, though the name trap with the Swedish geologists 
simply meant any compact dark-coloured rock composed of felspar 
with augite. 

Felstone is a compact, hard, flinty-looking rock, composed of 
acidic felspar and quartz. When this rock contains crystals of these 
minerals it is termed porphyry. 

Diorite consists of felspars, hornblende, and sometimes mica, being 
very nearly of the same constitution as granite, which it resembles 
very much, sometimes passing into that rock by metamorphic action. 
It is one of the most important and widely spread of rocks. Green" 



46 PHYSIOGRAPEY. 

Stone is a variety of this rock, in which green or dark-coloured 
hornblende predominates. Porphyrite consists of a matrix of basic 
felspar, containing felspar crystals, varying in colour from grey to 
dark purple. If such rocks as these contain mica as an essential it 
is called minette (Fr., pussy) ; if quartz, a quartz porphyry ; if augite, 
& basalt or dolerite. 

Kersantite is a minette, or micaceous diorite, consisting of mag- 
nesian mica, hornblende, &c. 

Melaphyre is composed of basic felspar, augite, magnetic iron 
(magnetite), and sometimes chlorite,* in a glassy base. It is of a 
black or dirty-green colour. Diabase is a similar rock, though 
differing a little in the species of the felspar. Pitchstone is a compact 
glassy kind of rock, somewhat like solid pitch in texture, its colour 
varying from nearly white to a dirty or blackish green. 

INTERNAL HEAT OF THE GLOBE. 

51. We will now consider the observations and evidences 
tending to prove the internal heat of the globe 

and that the heat increases the deeper we descend. That the 
earth was in amolten state at an early period of its existence, is strongly 
affirmed by its spheroidal shape, as any matter in a fluid state rotating 
on its axis would have a tendency to fly off from the equatorial 
region, bulging out there, on account of its centrifugal force, and 
flattening or compressing it about the axis of rotation. Active 
volcanoes point to the existence, at some unknown depths, of 
enormous masses of intensely-heated matter, which in many cases is 
in a constant state of fusion (lava). 

From observations made in mines and artesian wells, in France, 
England, Prussia, and elsewhere, it is assumed that below a depth 
of about 70 feet — the stratum of variable temperature — the tempera- 
ture increases on an average about 1° F. for every 60 feet in depth. 
The stratum of variable temperature is the crust of the earth as far 
down as the effects of the sun prevail — namely, about 70 to 80 feet — 
when we reach a constant temperature. Above this line the heat 
varies with the seasons. In the Astley Coalpit, Dukinfield, near 
Manchester, the hne of constant temperature was reached at the 
depth of 71 feet, being continually 51° F. At the bottom of the pit — 
namely, 2,080 feet below this line — the temperature is constantly 75°, 
showing an increase of 1° F. for every 86'6 feet. Observations taken 
at Eosebridge Colliery, near Wigan, on the rocks themselves, give 
the increase during the sinking there to be 1° F. for every 54*5 feet 

* Chlorite is a mineral composed of silica, alumina, and magnesia, of a 
greenish colour. 



PHTSIOGRAPHT. 47 

descended, the temperature at the depth of 2,418 feet being as high 
as 93-6° F. 

The water in artesian wells is warmer than the mean sur- 
face temperature, always increasing with the depth, the water in 
one at Grenelle, near Paris, whose depth is 1,800 feet, being con- 
stantly at 81-7° F. 

The density of the earth affords another argument in favour of a 
high internal heat. The average density of known rocks is about 
2"5 times that of water, and that of the whole earth about 5'5 ; but 
as the density increases with the depth, so much that water would 
be as heavy as mercury, or more than twice the specific gravity of 
the whole earth, at a depth of 400 miles, it is evident that if the 
interior of the earth be composed of such materials as occur at the 
surface, they would have a higher density still than this. Hence it 
is inferred that they must be greatly expanded by some expansive 
force or other, and the only force we know of capable of producing 
this expansion is heat. The chief facts regarding internal heat may 
be briefly expressed as follows : (1) The earth has an internal 
:emperature which increases everywhere with the depth. (2) The 
:ate of increase varies in different places; but in this country 
;he average increase is about 1° F. for every 60 feet in depth 
oelow the line of variable temperature. 

Chemical theories have also been put forth to account for the 
3xistence of internal heat, and consequently of volcanic action. 
The following may be mentioned : — 

Lemery attributes volcanic eruptions to the spontaneous combus- 
tion of materials existing near the surface, as sulphur and iron, beds 
of coal, &c. Brieslac supposes that volcanoes may arise from the 
mass of petroleum collected in cavities in the earth and set on fire, 
the combustion arising from the presence of certain combinations of 
phosphorus and sulphur. To substantiate his theory he calls atten- 
tion to the conflagrations that occur in coalmines, being set on fire 
by the presence of some body which must be spontaneously com- 
bustible. Other theories are put forth, but these two will be 
sufficient to give an insight into some of the supposed causes. 

52. The Nature of the Interior of the Earth.— It has long 

been inferred that the globe consists of a melted fluid core, enclosed 
in a cool and hardened rind or crust ; but this notion has recently 
been discarded. The principal objections that have been brought to 
bear against this theory are briefly as follow : (1) If the inside 
be liquid it must obey the sun and moon in their tide-producing 
action, causing corresponding undulations of the solid crust, 
especially at new and full moon. These certainly would have been 
perceptible if they existed. Sir William Thomson is of opinion 
that it is extremely impossible that any crust thinner than 2,000 or 



48 PHYSIOGRAPHY. 

2,500 miles could maintain its figure with sufficient rigidity against 
the tide-producing forces of the sun and moon. (2) If the volcanoes 
proceeded from one continuous fluid mass the lava would obey the 
well-known fluid law, standing at the same height in all cases, 
which is very far from the case, ^c. 

The more correct notion, and that which is most generally received 
now, is that the earth is a solid. In support of this theory it is 
supposed that the solidification of the earth commenced at its centre, 
and also at a later period at its surface by radiation. So that there 
would appear to be two zones of solidification, and between these 
we may imagine the space to be of honeycomb structure, containing 
the last remnants of the fluid in detached masses, which will account 
for the volcanic phenomena — those which have become extinct, 
probably through the fluid in the cavities becoming gradually solid, 
and others outbursting, perhaps due to an increased temperature 
brought about by some cause, such as the transference of the 
fluid from one part to another through this honeycomb structure. 

VOLCANIC PHENOMENA AND DISTRIBUTION 

OF VOLCANOES. 

53. The Phenomena of Volcanoes are the great commotions 

taking place under ground, ejecting through vents volatile bodies, 
melted rock (called lava), with fragments of sohd rocks, as cinders 
and ashes, and sometimes steam and sulphuretted hydrogen. The 
funnel-shaped depressed central openings through which the material 
is emitted are called craters (cups). Volcanoes are termed active 
when they are really in action, and extinct when they have ceased to- 
be active, but may become so at any time. There are also volcanoes 
which occur beneath the sea. These are called submarine (under the 
sea), and those on land subaerial (under the air). Volcanoes mostly 
appear in the form of cones, to account for which two theories have 
been put forth, namely, the elevation theory, and the eruption theory. 
According to the first it is supposed that the cone is formed by the 
swelling-up of the level lying rocks into a bubble-shaped mass, 
finally bursting at the top. These are known as craters of elevation. 
The eruption theory, however, is the one most generally accepted — 
namely, that the cone is the result of the ejected materials 
accumulating round the crater as a centre. 

Eruptions. — An eruptions is, in most cases, preceded by hollow 
rumbling noises, like thunder, and sometimes by earthquakes, dense 
black smoke hanging in vast heavy masses over the mouth of the 
crater. The snows that have been lying at the top melt, often 
causing sudden and destructive torrents, as in the case of the 
immense bed of snow upon Cotopaxi, in the Andes, being melted ia 



PHYSIOGRAPHY. 49 

one night (1803) ; and in 1797 the melted snow from Tunguarajagua, 
mixed with mud, &c., filling the valleys beneath to a depth of sis 
hundred feet. Flashes of flame, and enormous quantities of ashes, are 
projected, and often carried by the wind to an incredible distance. 
In the case of the eruption of Cosegunia, in the Andes, ashes fell at a 
distance of 1,200 miles. Red-hot stones, of great weight and size, 
are shot out of the craters like shells from an immense cannon, and 
are known as honibs. One of these, weighing ten tons, was thrown 
by Cotopaxi, in South America, a distance of nine miles ; the flames 
rose to the height of more than 1,000 yards from the crater, and 
the noise was heard more than 600 miles off, the ashes darkening the 
air for days. The lava flows down the sides of the mountains in 
immense streams. It is at first nearly of the consistency of honey ; 
hence its speed is not generally great, varying from two miles an 
hour to that distance in from one to ten years. The amount 
projected at one eruption is enormous, the greatest on record being 
from Skdpta Yokul, in Iceland, in 1783, when it flowed in two 
streams, 50 miles in one direction and 40 in the other, the breadths 
being 15 and 7 miles respectively, and averaging 100 feet deep. So 
that its immense volume might be better comprehended, it has 
been calculated that it would cover London with a mountain equal 
in height to the Peak of Tenerifie, or more than 12,000 feet high. 
The volcanoes of South America, and many others, generally 
discharge no lava, but simply ashes. 

54. Distribution of Volcanoes.— The chief fact regarding the 
distribution of volcanoes is their nearness to the sea, all — ^with the 
exception of two or three in Central America, and two or three in 
the range of Thian-Shan, in Central Asia — ^being near to the sea. 
Another striking feature is the tendency to a Hnear arrangement, 
as, for instance, in the great chain of the Andes and Asiatic Islands. 
Out of 407 active and extinct volcanoes, 365 are of this desci-iption, 
the remaining 42 being what is termed central, or central systems, 
consisting of a group of volcanic vents surroimding one principal 
cone, as those in the Canary Islands, with the central Peak of 
Teneriffe. 

The number of active volcanoes is variously estimated by different 
geograpl ers, but according to Professor Ansted they are distributed 
as folio va : — 

POSITION OF VOLCANOES. PBINCIPAL CONES. 

( Northern part 10 

Atlantic Ocean < Central part 10 

( Southern part 3 

GuK of Mexico — West India Islands 10 

Mediterranean Sea and coasts 5 

Bed Sea and African coast adjacent 2 

D 



50 PHYSIOGRAPHY. 

POSITION OF VOLCANOES. PEINCIPAL CONai. 

Indian Ocean— West side 3 

Asiatic continent..... 6 

Asiatic coasts and islands j Sou^l^ern part 75 

j Eastern part 110 

Eastern Archipelago and Pacific Ocean 16 

{Northern series 45 

Central series 45 

Southern series 54 

Antarctic Land 3 

Total 396 

from the above table we see that the greater number of active 
volcanoes belong to the islands and shores of the Pacific, forming, a3 
ic were, a helt to the basin of this ocean, and being at least two-thirds 
of the whole number. This hand or belt commences in the New South 
Shetlands, in lat. 62° 55' S., where there is an active volcano j 
passing from there to Tierra del Fuego, in Patagonia, and then on to 
the Andes, there being upwards of 30 in Chili, six or seven in 
Bolivia and South Peru, 16 or more about Quito, in Ecuador, nearly 
all above 14,000 feet high, the chief of which is Cotopaxi (18,876 
feet). Proceeding through Central America the line continues stili 
northward by the volcanoes of Mexico, where there are seven or 
more, passing through California, Oregon, and British Columbia, 
the Aleutian Islands, in which there are 23 volcanoes in a distance 
of 900 miles, carrying the chain across to Kamtchatka, on the 
Asiatic side of the Pacific, passing through the Kurile Islands, where 
there are 13, through the islands of Japan (24), through Formosa, 
the Philippines (15), to Moluccas, where it sends off a branch to the 
south east, through New Guinea, to New Zealand ; but the line of 
greatest activity continues westerly, through Java (45), to Sumatra 
(19), and afterwards in a north-westerly direction to Barren Island, 
in the Bay of Bengal. In the Indian Ocean there are a few, namely^ 
those in Madagascar and the Isles of Bourbon, Maiuitius, &c. 

Volcanic mountains, central systems, are found in the Sandwich' 
Islands, Marquesas, Society Islands, Friendly Islands, Feejees, 
Iceland (24), Azores, Canary Islands, Cape Verde Islands, Ascensiony 
Trinidad, Italy, Sicily, Mediterranean Sea, &c. 

The grandest examples of volcanic action are those in the Andes, 
next to which come those of Kamtchatka, Java contains more 
volcanoes than any area of the same size in the world. Of those in 
Europe the chief centres occur in the Mediterranean, namely, 
Vesuvius, Etna, and Stromboli, the last emitting fire aiid lava 
almost continuously — so much indeed that it is styled the lighthouse 
c£ the Mediterranean. Another of this description is Becla, Ju 



.PHYSIOGRiPHY. SI 

Iceland. To volcanic energy may be attributed the elevation and 
-subsidence of lines of coast, and the formation of numerous islands 
in different parts of the globe. Even hills of considerable size form 
in a short period, as, for instance, Mount Jorullo, west of the city 
of Mexico, which in 1759 rose out of the plain (and several square 
miles around it), in two days being raised 1,375 feet. Its height is 
now 4,265 feet. 

Solfataras are places where sulphur vapours escape and ncrusta- 
tions of sulphur form, though the proportion of this mineral 
small. Sometimes this gas also escapes from holes and fissures in 
the sides of the craters, the holes being then termed fuvieroles, or 
smoke vents. 

Jlot Springs or Geysers. — Springs of boiling water are to be 
found in some of the volcanic regions, the waters of which are 
mostly of a mineral character. In Iceland there is a group of fifty 
or more, called geysers (roarers), situated about 36 miles north-west 
'of Mount Hecla. The two largest are the Great Geyser and the 
Isew Geyser, about 100 yards apart, the former being 70 feet wide 
at its greatest diameter and 4 feet deep, situated on the top of a 
mound 15 feet above the adjoining ground. In the centre is a pit 
6 feet wide, and 80 feet deep perpendicular, up which the boiling 
water constantly ascends. At intervals of a few hours the water 
rises a little above the surface and then subsides, but is thrown 
generally once a day to a height of 60 to 80 feet, appearing as a lofty 
column of hot water. Sometimes these springs throw the water to 
a height of 200 feet, covering the country around with volumes of 
steam. Just previous to an eruption of this description the water 
was found at the bottom of the central pit to be more than 260° F., 
or 48° above the boiling point, though generally the temperature is 
from 180° to 190°. Hot springs occur at Bath and Buxton, in this 
country, the temperature of the water being 82° and 115° respectively. 
The propulsion of the water is supposed to be the sudden production 
of steam in subterranean chambers. Geysers are found in New 
Zealand and Cahfornia ; also hot springs in the Azores. "When the 
ejection of water is in a muddy area it forms mud volcanoes, or mud 
cones, examples of which occur in California, Iceland, on the Caspian, 
and along the northern slopes of the Himalayas into China. 

55. Earthquakes. — Earthquakes and volcanoes are evidently 
intimately connected, as the greatest number of earthquakes occur 
in volcanic districts ; but still they are not confined to these districts. 
These earthquakes consist of commotions, more or less violent, of the 
gurface of the earth. There are several kinds, namely, tremulouSf 
vertical, horizontal, and rotatory. The tremulous is the least destruc- 
tive. Vertical, or perpendicular ; a mine-like explosion, acting from 
below upwards, a c^se of this kind occurring at Eiobamba (1797), 



52 PHYSIOGRAPHT. 

when the bodies of the inhabitants were thrown on a bank nearly 
100 feet high. Horizontal^ or undulatory, resembling the undula- 
tions of the waves at sea, progressing at a speed of 20 to 30 miles a 
minute. Rotatory is the most destructive kind and most rare, the 
vibrations, following several cross directions, causing a whirling 
movement of the earth. The earthquake of Lisbon, in 1755, and 
that of Calabria, in 1783, were of this character. The direction of 
the concussions is generally in a linear direction, as that of 
Guadaloupe, in 1842, which extended a distance of 3,000 miles, wAth 
a breadth of 60 to 70 miles ; but sometimes circular, as at Calabria 
(1783), when all the villages within a radius of 22 miles were 
destroyed, and 100,000 persons perished, and fields even were found 
to have changed places. 

The most destructive earthquake experienced in the Old World was 
that of Lisbon (1755), when 60,000 persons lost their lives, the 
shock being felt over an area more than three times the size of 
Europe — rocking the waters of Lake Ontario, in North America, 
causing the Atlantic to overflow many of the West India Islands, 
the waves rising 60 feet above their usual level at Cadiz, and even 
8 to 10 feet on the Cornish coast. 

Earthquake Bands. — The regions where earthquakes occur are 
generally the same as the volcanic districts, the most noted in 
America being along the east, on the west side of the Andes. Severe 
shocks are also felt in the Alleghany Mountains. In Europe the 
chief seats are in the district of the Mediterranean, though there is 
an important one extending from Portugal to the Azores, Canaries, 
and the district of Central Asia, stretching from these places as far as 
Lake Baikal. The district of Iceland also includes the North of 
France, Great Britain, Denmark, and Scandinavia. Africa experiences 
vory few earthquakes, with the exception of the extreme north and 
f outh ; and Australia very few, those being in the west, but New 
Zealand frequently. 

Causes of Earthquakes and Volcanoes. — It is believed thai 
both earthquakes and volcanoes are due to the same cause, but what 
this cause is does not seem definitely known. The ancient 
philosophers were of opinion that their origin was due to some 
sudden explosion in the internal parts of the earth ; others supposed 
something in the air caused them, on account of earthquakes being 
preceded by a calm and serene atmosphere. The geologists of the 
present day are of opinion that the chief cause of volcanic eruptions 
and earthquakes is the expansive force of steam. The earth, as before 
stated, is supposed to be solid, with the exception of large 
cavities or lakes of molten lava. The water of the ocean and land, 
sinking through the crevices, constantly finds its way down, 
and is then converted into steam, whose enormous pressure is most 
probably the cause of both volcanic energy and earthquakes 



PHYSIOGRAPHY. 53 

Mitchell, in his work on earthquakes, expressed a somewhat 
similar opinion, attributing them to subterranean fires, whose 
existence in nature (he writes) we have certain evidence of, and 
which are capable of producing all the appearance of these actions. 
If a large quantity of water should be let out upon these fires 
auddenly, it may produce a vapour whose quantity and elastic force 
may be fully sufficient for that purpose. It is believed that the seat 
of the disturbing force is never above thirty miles below the earth's 
surface. The effects of earthquakes are, the elevation and depression 
of great areas of land, violent oceanic movements, the opening 
of great fissures (as in Calabria), and the swallowing up of whole 
cities and even mountains. 

THE EARTH'S CRUST. 
56. Slow Upheavals and Subsidences of the Earth's 

Crust. — That the level of the earth changes is evident from the 
fact that the greater portion of the land consists of strata composed 
of waste matter accumulated at the bottom of seas that have existed 
where the rocks are now found ; and even on our own coast, forests, 
&c., have been found submerged. We have evidence that slow 
upheavals and subsidences are constantly going on over large tracts 
of land. The shores of Scandinavia, on the Baltic, afibrd strong 
testimony of this, as in the southern extremity the land is gradually 
sinking beneath the sea, while at the north, in the district of the 
North Cape, it is rising as much as five feet in a century. These 
facts regarding the elevation have been drawn from the appearanco 
of the rocks above water, which were always formerly submerged, 
channels becoming shallower, and the occurrences of sea-beaches at 
elevations above the sea-level, which are termed raised heacheSy 
several of which are found on our own shore, namely, in Sussex, 
Devon, and Cornwall — the opposite appearances showing the 
depression. Another instance of slow depression is afibrded on the 
south-west coast of Greenland, where the shore is slowly subsiding, 
buildings being submerged along the coast. 

Facts have also been discovered lately adding to the existing evidence 
that there is a rise of land going on in the southern circum-polar 
regions. In Australia, Tasmania, and New Zealand the phenomena 
are remarkable. For instance, in one place certain lakes and a river 
disappeared, owing to the rise of the land. In another place, on the 
western coast of New Zealand, the high water mark oi the year 
1814 is now 200 yards inland. Many other facts might be cited. 
According to Mr. Howorth, in his communications to the Eoyal 
Geographical Society, they prove that the masses of land round 
about the south pole are at present " areas of upheaval," and 
that the earth's periphery is being stretched or extended in the 



54 PHTSIOGBAPHT. 

direction of the shortest axis. One remarkable fact to be noticed in 
all this area, exhibiting so many signs of rapid upheaval, is the 
marked absence of volcanoes, as in the entire circle there are only; 
the two or three in North Island, New Zealand, and those m- 
Tierra del Fuego. 

Many other instances might be mentioned bearing similar testi-: 
mony. The most striking proof of the depression of large tracts is, 
afforded by the distribution of coral reefs. These reefs are of three 
chief '^ij[idiS— fringing reefs, harrier reefs, and atolls. The coral 
polyps, or reef-builders, are unable to live in water when the depth 
exceeds 30 fathoms. Hence these reefs cannot commence to form, 
in the deep ocean, as they must have land within a few fathoms of, 
the surface to start on. Fringing reefs are of no great thickness, and 
skirt the coast at a small distance from it, as the reef around the 
island of Mauritius, which lies half a mile from the shore in very 
shaHow water. Barrier reefs are much greater reefs, occurring quite 
away from the shore, generally running parallel to the coast, the verti- 
cal thickness of the formation in some cases being quite 1,000 feet. 
Examples of this kind are — (1) The Great Barrier which extends in 
a broken line along the north-east coast of Australia, at an average 
distance of abo*ut 30 miles, though in some parts from .50 to 70, tho 
depth of water being from 30 to 00 fathoms, and otitside the reef the 
depth in some places exceeds 300 fathoms. (2) The reef off the 
west coast of New Caledonia is 400 miles in length, and distant 
from the shore about 10 to 16 miles, the depth on the side away 
from the shore exceeding 1,000 feet. Atolls are ring-shaped reefs 
enclosing a lagoon of still water. The outer slope of the reef is veiy 
steep, as in the case of the Cocos Atoll, where no bottom was found 
at a depth of 7,200 feet. The water in the lagoon is shallow. In 
the above-mentioned island it varies from three to ten fathoms in 
depth. From the known fact of the coral builders being unable to 
live below 90 or 100 feet, it is evident that the bottom on which 
these barriers and atolls were commenced building must have been 
gradually sinking for ages. According to the theory of Mr. C 
Darwin each atoll and barrier reef began as a fringing reef round 
an ordinary island. First the insects built the fringe reef close to 
the shore, the island slowly sinking, leaving a smaller surface and 
causing more space between it and the reef — the insect still building 
upwai'ds, forming a hart ier reef, the land continuing slowing sinking 
until the island has entirely disappeared beneath the waters ; at the 
same time the reef, continuing to grow upwards, left at the surface 
a ring of coral around a lake. 

ProhaUc Cause of the Movements of the Earth's Crust. — The 
general opinion is that the slow upheavals and subsidences are con- 
sequent on the contraction of the earth by cooling — the warm interior 



PHYSIOGRAPHY. 55 

loses heat faster thsCn the comparatively cold exterior, and contracts 
more than the outer part, which tries to follow the interior but 
cannot, owing to its curved form, except by bulging ap in other 
places. In this way continents may sink, and the bottom of the sea 
may be raised above the level of the water. 

RELATIVE AGE OF STRATA. 
57. Changes the Earth's Surface has Undergone, and in 

the Forms of Life. — That the surface of the earth is continually 
imdergoing changes is evident from the upheavals and subsidences 
that are going on continuously, and by the different strata that 
appear above each other. If we examine the mud and sands of our 
coasts and seas we find. imbedded in or resting upon them relics of 
many living species of animals and plants. On examining sandstones 
and clays we find, too, they are associated with organic relics, the. 
beds of coal and peat, &c,, revealing the same facts. Hence we 
come to the conclusion that these deposits or strata are the result of 
forces tending either to break up and remove, or to deposit and 
consolidate in new forms. Where dry land is at the present day W3 
have strong evidence that it has been the bottom of the sea at 
some previous date. The agents causing these changes on the earth's 
surface are : (1) Aqueous, forming sand and mud banks, &c. 
(2) Igneous, causing the lavas, &c., issmng from the volcanoes and 
earthquakes. (3) The works of the polyps in forming reefs, and the 
chalk-forming animals, Foraminifera. 

When one stratum rests upon another we come to the conclusion 
that the lowe?^ bed was deposited before the icpper bed was com- 
menced. In this way geologists are able to arrange the strata 
composing the earth's crust in a series commencing from the oldest, 
or first formed, up to the newest, or last formed. They are also 
guided by the fossils appearing in them ; for if rocks of the same 
age or formation are examined we may find some local fossils — ^yet 
many are constant — occurring wherever the rocks are found ; but 
in passing to a newer rock there appears a complete change in the 
fossils, which not only proves it to be of a different formation, but 
that each as:e was characterised by its own peculiar fauna (animals) 
a.nd flora (flowers), one animal or plant after another disappearing 
and new species taking their places. 

The stratified rocks fall into three great divisions — namely, the 
Cainozoic, or new ; the Mesozoic, or middle ; and the Palaeozoic, or 
ancient group. The first division includes the Tertiary and Quar- 
tenary, the second (Mesozoic) the Secondary, and the last, Primary, 
or the oldest strata of which we have any knowledge, each division 
representing, as nearly as can be determined, a different arrangement 
of sea and land. 



56 PHYSIOGRAPHY. 

The following table gives the names of the different formations, or 
systems, arranged in the order of the superposition, the oldest being 
at the bottom and the youngest known at the top : — 
III. — Catnozoic (Recent Life). 

Post-tertiary, or Eecent Accumulations — Alluvium, fen deposits, 
river gravels, &c. 

Tertiary — PKocene — Crag ; Miocene — ^Bovey-beds, &c. ; Eocene — 
Fluvio, Maine series, &c. 

II. — Mesozoic (Middle Life). 

Cretaceous, or Chalk System — Chalk, greensand, Wealden, &c. 

Oolitic, or Jurassic System — Oolite, Has. 

Triassic, or Upper New Red Sandstone. 

I. — PALiEozoic (Ancient Life). 

Permian, or Lower New Red Sandstone — Magnesian limestone 
series, &c. 

Carloniferous System — Coal measures, mountain limestone, &c. 

Devonian, or Old Red Sandstone. 

Silurian — Cambrian and Laurentian. 

In the last (Palgeozoic) group of formations the forms of life differ 
greatly from what are on the earth now, and are stni different in the 
middle division, but not so strange in aspect. In the first, or 
Cainozoic, we have those that exist at present, the oldest of which 
is the Eocene, containing a few species of shells that now exist ; 
the Miocene stUl more ; the Pliocene, containing the more recent 
descriptions, though a number of the mammalia that then existed 
are now extinct. 

In the SiLUKiAN Age, trildbites, a peculiar form of Crustacea, 
abounded, also graptolites, &c. The Old Red Sandstone is sometimes 
caUed the age of fishes, on account of the numerous remains which are 
found in this system. The fishes were mostly of the ganoid type, being 
cased in bony enamelled plates. Other kinds are the placoid, the 
skin being dotted something similar to the shark, the chief of which 
were the asterolepis, a fish 20 or 30 feet in length; holoptychius, 
another large fish, with wrinkle-like marks on its scales ; ptei^chthys, 
cephalaspis, osteolepsis, coccosteus, &c. 

The Carboi^iferous System contains coral fossils, such as syHn- 
gopora, litkostrotion, Sec, shells, a,s spirifera Sind productiis, archemedi' 
pora, euomphalus, hellerophon, goniatites, and nautilus. Of the coal 
measures in this system the chief fossils are plants. Among the most 
important are stigmaria, or roots of plants ; the sigillaria, or the 
stems ; and lepidodendron, so called from its scaly bark. The fronds 
of tree-ferns are numerous, such as pecopteris and neuropteris, figured 
kinds ; sphenopteris, cyclopteris, odontopteris, &c. 

Permian System. — The fossils of this formation are not very 
abundant, but those which appear are associated with a considerable 
change of species, many species of fauna finally disappearing. Among 



PHYSIOGRAPHY. 57 

the cHef fossils are fenestella (Polyzoa), prodnicttts horridus, spin/era 
alata, &c. (Brachiopoda) ; schizodus,BaJcevelUa,pecten,&c.{ConcbJ£eTa) ; 
Palceoniscus, platysomus, &c. (Fishes). 

Triassio System. — Some of the fossils of this system are ceratites 
nodosus, characteristic of the shells ; estheria minuta (Crustacea), 
and microlestes antiquus, a little beast of prey, the earliest known 
mammal, something like a kangaroo. In this system reptiles became 
more numerous than in any earlier rocks, among which may be 
mentioned cheirotkerium or labyrinthodon, nothosaurus, and rhyu' 
cosaurus, Sec. The ammonites and belemnites make their first appear- 
ance also. 

JuBASSic OB Oolite and Lias System. — ^The lias is remarkable 
for its fossil reptiles. It, together with the oolite, has been caUed 
the age of reptiles, from the great development of those animals, 
both in size and number, of which the genera best known are the 
ichthyosaurus, plesiosaurus, and pterodactylus. The first of these 
was a lizard, somewhat like a fish, sometimes more than 25 feet in 
length ; the second had a swan-like neck, and nearly as long as the 
first ; and the last (pterodactylus) had wings, and could fly hke a 
bat. Beetles, crickets, and other insects, have been found in the lias 
formation ; oysters also are abundant. In the oolite ammonites and 
Memnites are very abundant, long-legged lizards appearing, and four 
species of mammals, aU pouched animals like the kangaroo, the 
eenera being amphitherium, phascolotherium, and stereognathus. 

Cretaceous System. — The cretaceous fossils, compared with the 
oolite, are new, not a single species of the latter occurring — the 
foraminifera now appearing, which resemble very closely those now 
living in the Atlantic and other seas. The large reptiles, ichthyo- 
saurus, &c., occur for the last time, in the white chalk, several new 
genera appearing, as the mososaurus. Birds also, about the size of 
a pigeon, have been found in the upper greensand. 

Eocene System (Tertiary.) — This period — ^namely, the tertiary — 
is sometimes called the age of mammals, among which may be 
mentioned coryphodon, somewhat like the Uving tapir, though larger ; 
hyracotheHum, allied to the hog ; palceotherium, or ancient beast, 
about as large as a horse, but Hke the tapir ; anoplotherium, with a 
long powerful tail, and many others. It is supposed that during 
this system the climate of England was tropical (like that of the 
East Indies at the present time), on account of the palms, crocodiles, 
turtles, &c., which have been found ; also that this country was 
joined to the Continent, the proof of which lies in the remains of 
large mammals making their appearance in different parts of the 
English deposits in the Eocine time, it being evident that these 
animals must have walked over. 

Miocene Period.— The plants and flowers of this period closely 
resemble the flora of the present day, being, among many others, 



58 PHYSIOGRAPHY. 

evergreens, oaks, -fig-trees, laurels, vines, palms, beeches, and trees 
of the cinnamon tribe. Among the mammalia there are dino- 
therium cheer opotamus, and others which are now extinct ; and the 
elephant, hippopotamus, rhinoceros, giraffe, monkey, deer, &c., which 
are living species. 

Pliocene Period. — The remains of the following mammals, 
among others, have been found in the English beds, or crags, of this 
period : IVhale, elephant, rhinoceros, tapir, horse, bear, pig, deer, 
hyena ; and the genera mastodon (allied to the elephant, but with 
very long tusks) and hijpparion (allied to the horse), both of which 
are now extinct. 

From the crags we learn that a portion of Norfolk and Suffolk 
were under the sea at the commencement of this period, these 
formations resembling those deposits now forming in the German 
Ocean. More than one-fourth of the fossils of these crags belong to 
extinct species. 

PosT-T£RTiAE,T, OR PosT-PLiocENE, PERIOD. — ^Remains of animals 
now inhabiting this country, with others inhabiting other parts of 
the world, and some altogether extinct, are found in the British 
formations of this period. Among the mammalia are the fox, wolf, 
hyena, reindeer, lion, hison, hippopotamus, two kinds of elephant, 
horse, pig, rabbit, squirrel, &c. We also meet with proofs of man's 
existence at this age by the disco vei-y of some of his works, such aa 
flint knives, hatchets, arrow heads, &c- In Continental gravels and 
caves of this age man's bones have been found side by side with 
those of the mammoth and other extinct animals. 

The Age of the Earth is not yet, and doubtless never will be, 
known, but many conjectures and calculations have been made 
regarding it, the chief of which are based on calculations made 
upon the heat of the earth, and the time it would take to cool from 
its molten state. From experiments made upon the cooling of lava 
and certain other rocks by Bischof, Professor Helmholtz concludes 
that the earth could not cool from the temperature of 2,000° C. to 
200° C. in less than 350,000,000 years, and scores of millions 
more must have elapsed to have reduced it to 94° C. — the highest 
heat at which it is estimated that animal and vegetable life could 
commence. Sir W. Thompson is of opinion that the solidification 
of the crust took place about 100,000,000 years ago, bringing the 
probable age of the earth to 500,000,000 years. Other evidence 
regarding the antiqmty of the globe is drawn from the effects of 
rivers in their action on the earth's crust. For example, it is well- 
known that the Falls of Niengara are now seven miles nearer Lake 
Erie than they have been at some previous date ; and taking six 
inches as the calculated rate of retrocession per annum it gives 
186,000 years as the time required for the river to have performed 
this worL 



PHTSrOGRAPHT. 59 

ASTEONOMICAL GEOGRAPHY. 



THE EARTH: ITS ASTRONOMICAL RELATIONS. 

It has been determined by astronomers that the earth we live on is 
one of a number of 'planets (wanderers) which revolve round the sun 
as a common centre, but at different distances and velocities. These, 
with their satellites, or moons, together with an unknown number of 
comets, constitute what is termed the solar system. 

There are at present known eight large or primary planets, which 
revolve round the sun in nearly circular orbits or paths, and 220 
asteroids — small planet-like bodies, which are all situated between 
the orbits of Mars and Jupiter, and are supposed to be fragments of 
an ordinary-sized planet, that has been disrupted. All the planets 
between the sun and this gap are called inferior or interior planets, and 
those beyond superior or exterior planets. There are 18 secondary 
planets, or moons, revolving round their primaries ; and an unknown 
number of comets, which revolve round the sun, but move in no fixed 
direction. The primary planets are Mercury, Venus, Earth, Mars, 
Jupiter, Saturn, Uranus, and JSTeptune, their names being written in 
the order of their nearness to the sun. Of the secondary planets, 
or moons, the Earth and Neptune have one each, Jupiter and Uranus 
four each, and Satirrn eight. The multitude of stars that move in a 
mass and keep their position with regard to each other, and to the 
Bun, moon, and a few others, are called fixed stars. 

58. Form and Motion of the Planets.— The planets are 

all round bodies {spheres, or more correctly spheroids, like the 
earth, owing to the effect of centrifugal force — that is the force 
which causes all matter when spinning round to have a tendency to 
fly off in a straight line.) They have two motions. First, their 
motion round the sun, and secondly, their revolutionary motion on 
an axis, travelling in both cases from west to east, each revolution 
being termed a day. The paths or orlits that they describe in their 
journey round the sun are elliptical — that is, the figure described 
is an ellipse,* though differing very httle from a circle, or having 
very little eccentricity. 

The cause of the planets moving in elliptical paths is the result o£ 
two forces acting on the planet at the same time, but in different 
directions. These forces are the centrifugal (or tangential) and the 

* An ellipse is a plane figure bounded by a curved line, and is sucb that if 
from any point in the curve, two straight lines be drawn to two certain points, 
the sum of these lines will always be the same. These two points are called 
the foci of the ellipse, and the distance *-H>m the centre of the ellipse to either 
of its foci is called the eccentHciti/. 



60 



PHYSIOGRAPHY. 



centripetal. The former would, if not counterbalanced by some other 
force, cause the earth to move right away from the sim, but this is 
balanced by the centripetal force, which always acts at right angles, 
proceeding from the attraction of the sun. This force, if also 
unopposed, would by the laws of gravitation (15, 16) cause the planet 
to move towards the sun with a continually accelerated speed. But 
with the two forces acting on it at the same time it obeys neither, 
following, according to the jparallelogram of forces (7, 8), a mean 
course, describing a curved path, which in all cases is one of the 
conic sections, its shape depending on the direction, distance, and 
Telocity.* 

In the annexed figure let E represent the earth, and s the sun ; 
then, supposing the earth to be moviag in a straight hue, with a 
velocity sufficient to carry it to A in a given time, during which the 
E ^ sun's attraction acts upon 

E with sufficient force to 
bring it to B, the earth 
will describe the diagonal 
of the parallelogram 
EACB, though it doea 
not pursue a straight 
line, as in Fig. 1, page 9, 
but a curve, owing to the 
sun's power of attraction 
acting continually on 
the earth, and thereby 
causing a deviation from 
the right line. In an 
exactly similar manner 
the earth performs the 
^ff- 5. curves CH, HN, &c. To 

understand more correctly how it is that the line is not a right 
line it must be remembered that the attraction of the sun is not 
exerted at once, or by a single impulse, but by degrees, being constant. 
Hence we may suppose that the parallelogram EACB is made 
up of an infinite number of minute parallelograms, and that the 
cur ved line likewise consists of an infinite number of diagonals. 

Kepler's laws of elliptic motion are : (1) " That every planet 
moves so that the radius vector, or liae drawn from it to the sun, 
describes about the sun areas proportional to the times. (2) That 




*Let d=diameter of the circle ; a, the centrifugal force ; 6, the centripetal ; 
V and r 1 , their respective velocities ; then the path is a circle when v^=dxvi; 
an elli])se, when v^> (is greater than) dy.v ; a parabola, when v'=2 fdxvj/ 
an hyperbola, whenr2>2 (dxv). In every case the angular velocity of the- 
radius-vector must he inversely proportional to the square of the mutual 
distance of the two bodies. 



PHYSIOGRAPHY. 61 

the planets all move in elliptic orbits, of which the sun occupies 
one of the foci. (3) That the squares of the times of the revolutions 
of the planets are as the cubes of their mean distances from tha 
sun." From the first of these ]!!fewton concluded " That the force 
acting on the planets is directed towards the centre of the sun ; " 
from (2), " That the force acting on the planets is in inverse ratio 
of the square of the distance of their centres from that of the sun ;" 
and from (3), "That the force is proportionate to the mass." 
(See 15, 16.) 

The point of the planet's path farthest from the sun is called its 
Aphdion, and that nearest the sun its Perihelion, the sun being 
continually in one of the foci. 

Sun and Moon. — Of the heavenly bodies, the two that 
concern us most, as relating to Physiography, are the sun and 
moon, more especially the former, the centre of our universe 
and of this earth's annual revolution, being the source of heat 
and light, and the chief agent in sustaining life. The diameter 
of the sun is about 852,680 miles, or 107 times the earth's 
diameter, being equal in hulk (not mass) to about 1,249,500 earths ; 
but its mass, or weight, is equal only to about 315,115 times 
that of this earth. Hence the materials composing the sun have 
only one-fourth the density or weight of those composing our planet, 
that is bulk for bulk, being about 1*43 times the density of water. The 
force of gravity at the sun's surface compared with the earth is 27 ■2.* 
The distance of the sun from the earth is calculated to be, by recent 
observations, about 91,430,000 miles ; and from the spots on the sun it 
has been determined that it revolves upon its axis in 25 days 7 hours 
48 minutes. Some of the spots seen on the sun are enormous in 
size, many being recorded varying from 30,000 to 45,000 miles in 
diameter. The appearance of these spots is generally a very dark 
central space, of tolerably regular form, surrounded by a more 
irregular belt of semi-luminous matter. The interior is called the 
nucleus of the spot, and the exterior the penurribra. The spots have a 
maximum and a minimum frequency of about eleven years, corres- 
ponding with the magnetic disturbances, as a precisely similar period 
is known to exist in the variation of the magnetic declination, the 
maxima and minima agreeing exactly with those of the spots. 

Effects op Sun" Spots ok Climate. — This question has often 
been discussed, though as yet our knowledge on the point is very 
scanty, and it is probable many years will elapse before it can be 

* Gravitation proceeds from its centre. Hence, distance that bodies at the 
surface are removed from the centre of attraction is about 426,340 miles, and 
its mass, or gravity, 315,115. Hence, by the laws of gravitation (16), the 
gravitation of the stm, compared with that of the earth, is as the square of 
the radius of the sun : square of the radius of the earth : : 815,115 ; or as 
426,3462 : 3^9562 -. ; 315,115 ; 27-2. 



62 PHTSI0GRAPHY. 

answered fully. Professor Langley, of Alleghany Observatory, 
Pennsylvania, states, from Ms own investigations, that sun spots do 
exercise a direct and real influence on terrestial climates by de- 
creasing the mean temperature of this planet at their maximum. 
The decrease is very minute indeed, the whole effect being repre- 
sented by a change in the mean temperature of our globe in eleven 
years not exceeding three-tenths, and not less than one-twentieth 
of one degree of the centigrade thermometer. 

That the sun has a motion through space is now an established 
fact, travelling at the rate of 18,000 miles an hour, or 155,000,000 
miles per year, 

59. The Photosphere and Cromosphere of the Sun — 

Whenever the sun shines we see a kind of brilliant envelope, called 
the photosphere or light-giving surface, it being the shining surface 
of the sun. This is it from which we derive our light and heat. 
The faculce, or brighter portions of the sun's surface, appear to be 
elevated masses of luminous matter when viewed stereoscopically ; 
and as they remain for days suspended in the same position they are 
probably gaseous or vaporous. From observations witnessed daring 
total eclipses of the sun it has been ascertained that the sun pos- 
sesses an exterior gaseous envelope, of great extent, above the photo- 
sphere, probably extending more than 800,000 miles. During an 
eclipse, at the moment the last remnant of the photosphere is hidd en 
by the dark moon, there appears a kind of white halo at the up')er 
part of this gaseous envelope, or atmosphere, called the corf ma, 
which may be regarded as a reflection of the sun's light by hit 
atmosphere. The lower regions of this corona is composed of layers 
of a greatly heated gas, of extreme tenuity, entirely surrounding the 
sun. This is called the chromosphere, and is subject to the disturb- 
ances of the photosphere, which appears to be in a constant state of 
agitation, causing the chromosphere to be thrown about in huge 
•masses, in the shape of red flames, often to the height of 100,600 
miles. There is supposed to be yet another layer of very highly 
heated gas, so hot, in fact, that metals such as iron continue in a 
state of vapour. Regarding the intensity of heat proceeding from 
the sun, it has been calculated that the annual heat is 2,381,000,000 
times that received by us ; and that received by the earth in one 
year would be sufficient to melt a layer of ice 114 feet thick all over 
the earth's surface. The light proceeding from the sun has also 
been proved to be 618,000 times that of the full moon, and equal to 
6,560 wax candles at a distance of one foot from the eye. 

The sun has been found, by the aid of the spectroscope, to be 
composed of similar material to the earth. Among the elements 
that have been ascertained may be mentioned hydrogen, iron, sodium, 
magnesium, manganese, calcium, chromium, barium, copper, nickel, 
&c. 



PHT3I0GEAPHT. 63 

60- The Moon. — 'Thin satellite revolves round tlie earth in an 
elliptical orbit, the earth being one of the foci, and carried with it 
round the siin. It takes the moon 29 days 12 hours 44 minutes 
2"87 sBConds to complete its circuit, returning to the same position 
with regard to the earth and sun. This period is called a lunar month, 
or lunation. The time of the moon's rotation is exactly the same as 
the time of its revolution round the earth,, and in consequence of 
this fact the moon always turns the same side to the earth. Its 
diameter is 2,160 miles, or a little more than one-fourth that of the 
earth ; its distance from the earth being 238,851 miles, or 60 
times the earth's radius, and specific gravity '61. The surface of the 
moon is very diversified, as seen through the telescope, high 
mountains existing which throw long black shadows. From the 
length of these the heights of many mountains have been measured, 
the highest points reaching nearly 23,000 feet high. They are 
supposed to have been raised by volcanic agency, as most of them 
have large crater-like basins. The light we receive from the moon 
arises not from its own surface but by reflected solar light. 

The phases of the moon prove it to be a spherical body illumined 
by the sun. When in conjunction with that luminary the moon is 
invisible. "When moving from the sun towards the east it is first 
visible, it being now called the neiu moon, and appears as a crescent ; 
when 90° from the sun — namely, at a right angle — there appears a 
half moon ; as it recedes farther it is gibbous ; when in opposition it 
shines vdth a full face, being then called full moon. On its journey 
towards the east, approaching the snn, the appearances are just the 
reverse, first being gibbous, then halved, and lastly a crescent, after 
which it disappears from the superior brightness of the sun and 
the smallness of the iUumiued part turned towards the earth. 

THE EARTH— ITS FORM AND MOTIONS. 
61. The Form or Shape of the Earth is nearly that of a 

globe or sphere, or more correctly an oblate spheroid, being flattened 
it the poles, probably through the effect of its centrifugal force. 

Among the many proofs put forth regarding the rotundity of the 
earth, may be mentioned : (1) A vessel sailing away from the land 
does not become lost from view on account of its distance, but 
gradually sinks out of sight ; first losing sight of her hull, next her 
lower or main sails, and lastly her top sails, thus showing that she 
is passing over a convex surface. (2) By employing a surveyor's 
level upon the surface of the water of a canal it will be found that 
at the distance of one mile the water is depressed below the level of 
the instrument about 8 inches, which is called the dip. This not 
only proves that the earth is round, but also gives the diameter of 
Buch a globe that will have a curvature equal to this, namely, 7,920 



C4 PHYSIOGRAPHY. 

miles,* wMcli is not very far from the mark, the true dip being 
7'9821 inches. (3) In travelling any considerable distance, either 
north or south, new stars gradually appear in the direction in which 
the person is travelling, and those behiad disappear. This is exactly 
what would happen if the earth was round, and under no other 
circumstances, hence we conclude the earth must he round. (4) The 
shadow cast by the earth on the moon during an eclipse is always 
circular, which could not be the case unless the world was round. 

62. The Size of tlie Earth. — Owing to the earth being 
correctly a spheroid, its polar diameter is greater than its equatorial 
diameter. According to Airy and Bessel the true dimensions are : — 

Polar diameter 78991 miles. 

Equatorial diameter , 792o"6 „ 

Difference, or polar compression 26*5 „ 

Proportion of diameters, 298 to 299, the polar 
diameter being -^g shorter than the equa- 
torial ; hence the mean diameter is 7912'35 „ 

The circumference of the earth is 24,856 miles ; the area of its 
surface, or superficial contents, 197 million square miles ;t the volume, 
or soHd contents, 259,000 million cubic miles ; and weight, taking the 
density to be 5| times that of water, 5,852 trillion (5,852,000,000, 
090,000,000,000) tons. 

The density of the earth, as compared with the materials at its 
surface, has been estimated with considerable precision : (1) By 
observing the attraction exercised by a mountain on a plumb-line, 
as compared with the earth's attraction upon it ; (2) By calculating 
the effect of the increased and diminished distance from the earth's 
centre, on the vibration of pendulums, vibrating above and below 
the surface ; and (3) by comparing the attraction of large balls, whose 
weight and density are known, upon a freely suspended bar, with 
the attraction of the earth upon the ball. From these experiments 
it has been found that the mean density of the rocks at its surface 
is about 2^ times that of water at the temperature of 62°F., and that 
of the whole mass about 5^ times (5'675) that of water. Taking the 
earth's density as 1, the density of the Sun is '25, Moon '63, Mercury 
1*24, Venus *92, Mars "52, Jupiter '22, Saturn '12, Uranus '18, and 
Neptune 'l?. 

*By a well-known property of the circle we have: 2 (the radius - dip! 
+ dip : length of surface measured : : length of surface measured : the dip. 
Let a; = number of feet in radius, then we have 2(a;-|) +§ : 1760 X 3 :: 
1760 X 3 : ? : that is f x -i= (1760 X 3 x 1760 X 3) feet ; hence x = 

^T^P^^-^ ITg O X 3 X Z -i'jQQ X 9=3930 miles ; .'. diam.=3960 x 2=7,920 milea 
1760 X 4 ^ ^ 

t Surface of a sphere = square of diameter multiplied by 31416. Solid 
contents of a sphere = cube cf diameter multiplied by '5236. 



PHYSIOGRAPHY. 



65 



63. Motion of tlie Earth. — The earth has two motions, namely, 
its annual motion round the sun, in about 365^ days, or, more 
precisely, 365 days 5 hours 48 minutes 51 '6 seconds. This is called 
a year. Secondly, its diurnal, or daily motion, or rotation on its own 
axis, in about 24 hours, or, more correctly, 23 hours 56 minutes 
4 seconds, causing day and night, and the apparent rising and setting 
of the sun. At the equator any spot moves at the rate of more 
than 1,000 miles an hour, the velocity decreasing as we travel towards 
the poles, Great Britain travelling about 600 miles per hour, or ten- 
miles per minute. Also the earth's velocity in its orbit round the 
8un is 65,533 miles per hour, the distance it travels La the yearbeing, 
about 574 mUlion miles. 

64. Day and Night. — During the earth's rotation on its axis 
only one-half of its surface can be exposed to the sun's rays at any- 
one time, this being lighted while the other half is in darkness. 
But the length of day and night varies according to the seasons, the 
chief causes of which are, first, that the orbit of the earth's revolu- 
tion round the sun is not a perfect circle, but an ellipse ; secondly, that 
the earth's axis in performing this revolution is not perpendicular, 
but inclined to an angle of 66° 32' to the plane of its orbit, or 23^**' 
(23" 28') to the equator. The diagram accompanying will assist in 
explaining the effects of this elliptical orbit and the incHnation of its 




65. Seasons. — ^The earth is represented at four different positions 
in its yearly orbit, S being the sun, A representing the position at 
the vernal equinox. The whole hemisphere from pole to pole is= 
illuminated by the sun, so that during the rotation every part ol the 
earth will have an equal share of light and darkness, day and night 
E 



66 PHYSIOGRAPHY. 

being equal. Similar at B. At any other position day and night 
are respectively shortened and lengthened. When at D, the 
Slimmer solstice for the northern hemisphere, the south pole will be 
in darkness, and within a cu'cle of 23J° at the north pole the sua 
will not set. When at C it will be just the reverse. When the part 
presented to the sun is at a — namely, on the 22nd of December — 
it is midsummer to all the southern parts of the earth and winter 
to all the north, and as it gradually proceeds on its journey towards 
6 the northern regions gradually receive more and more heat and 
longer and longer days, till their midsummer comes on the 21st of 
June, being just tA reverse with the southern regions. 

Nutation. — If the axis of the earth were perpendicular, instead of 
being inclined, the length of the day would be always and everywhere 
the same, and we should have no change in the seasons. Hence, if- 
the angle of inclination should change it is evident it would cause a 
change in them ; and this does actually take place. The angle at 
present is 23° 28', but it gradually decreases — namely, at the rate of 
about 48" in a century — diminishing for an immense period, after 
which it will begin to increase again — that is, the axis itself revolves 
in a small ellipse, but does not always point exactly to the same place 
in the heavens, thereby causing the variation in the obliquity of the 
ecliptic. This motion is termed nutation,* the cause of which is the 
influence of the planets upon the earth. The circle described is 
about 2° 42' in diameter, its revolution occupying a period of about 
270,000 years. 

Precessional Motion. — Besides the above there are other 
movements, the chief of which is that called the -precession of the 
equinoxes — that is, they precede their time. This movement is 
caused by the attraction of the sun and moon on the equatorial 
regions — namely, on the portions of the earth which the centrifugal 
force have caused to bulge out, the effect of which is that the 
equinoctialf points move westward (recede) 50 ■224" per annum, 
causing the equinox to occur nearly 20 minutes earlier than it 
otherwise would. Hence, in the course of ages summer will be 
where winter is now. This movement, uninjlaenced by any other 
motion, would cause the equinoctial points to perform the circle of 
the equator in a period of 25,868 years — that is, the seasons toill 
coincide with each part of the orbit once in that period. But this 
movement is influenced by another motion, the result of which is 
that this cycle of changes is shortened. The latter motion is termed 
the revolution of the apsides,^ caused by the attraction of the planets. 
The apsides are the points at which the earth is nearest and farthest 
from the sun. The line connecting these points is called the line of 

* Nodding. f The points where the ecliptic crosses the equator. 
, t A curve. 



PHYSIOGRAPHY. 



67 



tht apsides. Tliis line does not keep continually directed towards 
the same point in the heavens, but slowly revolves ; and the result 
of the combination of this revolution with the precession causes the 
cycle of the seasons to be performed in about 21,000 years, or 4,868 
years sooner than it otherwise would. 



PHYSICAL GEOGEAPHY. 



THE SURFACE OF THE EARTH— DEFINITIONS. 

MATHEMATICAL DIVISIONS OF THE EARTH. 

The Axis of the Earth is an imaginary line passing throngh its 
centre, and round which it rotates daily. 

The North and South Poles are the extreme points of its axis. 

The Equator is a great circle passing round the middle of the 
earth at equal distances from the poles, dividing it into two equal 
portions, the northern half being called the Northern Hemisphere, 
and the southern half the Southern Hemisphere. 

A Hemisphere is one-half of a sphere. Hence, considering the 
earth as as a sphere, it means one-half of it. 

The Meridians are great circles passing round the earth at right 
angles to the equator, and cutting each other at the poles. 

Latitude is the distance 
of a place north or south 
of the equator. 

Longitude is the dis- 
tance east or west of 
any given meridian. 
Longitude is reckoned in 
this country from the WEST 
meridian of Greenwich, 
which is called the first 
meridian. 

The Tropics are two 
circles drawn parallel to 
the equator, namely, the 
Tropic of Cancer, 'about 
23i° north of the equator 



WOR TH POL E 




EAST 



SOOTH FQUC 

Fig 7. 



and the Tropic of Capricorn, about 23J° south of the equator. 

The Polar Circles are two lines drawn round the earth parallel 
to the equator, namely, the Arctic Circle, nearly 23^° from the 
north pole, and the Antarctic Circle, nearly 234** from the south 
pole. 



•68 PHYSIOGRAPHY. 

The Ecliptic is a great circle cutting the equator at an angle of 
23 g° at two opposite points, reaching the tropics as its extreme limit, 
north and south. It represents the sun's apparent path in the 
heavens, but in reality the path of the earth round the sun. 

The points where the ecliptic cuts the equator are called the 
Equinoctial Points or Nodes, because, when the sun is in these parts 
of his course, the day and night are equal. These equinoxes take 
place twice a year, namely, on the 21st of March, and 21st of 
September. 

The Zones are five great helts into which the earth is divided by 
the tropics and polar circles. (1) The Torrid Zone, between the 
tropics, so called on account of its great heat, through the sun being 
always vertical in some part of that space. (2) The spaces between 
the tropics and the arctic and antarctic circles on either side, are 
called Temjperate Zones (north and south), having a milder or tern- 
perate climate. (3) The spaces between the polar circles and the poles 
are called Frigid Zones, from their extreme cold. The breadth of each 
of the torrid zones is about 1622"5 miles ; of each temperate, about 
2969 miles ; and of each frigid, 1622'5 miles. Hence, calculating 
their respective areas, we have — 

Sq. miles. Parts 

North Frigid Zone 8,132,797 .. ..Or 4\ 

North Temperate Zone 51,041,592 26 f 

Torrid Zone 78,314,115 40 VOut oi 100, nearly. 

South Temperate Zone 51,041,592 26 I 

South Frigid Zone..... 8,182,797 4/ 

Total .*. 196,662,893 ICO 

NATURAL DIVISIONS OF THE SURFACE OF THE 
EARTH. 

A Continent is a large continuous extent of land, including 
Beveral countries, as Europe, Asia, &c. 

An Island is a smaller extend of land, and entirely surrounded 
by water, as Great Britain, Ireland, Sicily. 

An Archipelago consists of several clusters or groups of islands, 
this name was originally applied to the Gulf of the Mediterranean, 
between Greece and Asia. 

A Peninsula is land almost surrounded by water, as England, 
Italy. 

A Cape is a head or point of land stretching out into the water, 
as Cape of Good Hope. Other names of Capes are. Promontory, 
Head, Headland, Point, Naze, Ness. 

An Isthmus is a narrow neck of land uniting two larger portions 
together, as the Isthmus of Panama, between North and South 
America. 



PHYSIOGRAPHY. 69 

A Coast or Shore is tlie part of a country bordering on a sea, 
lake, or river. 

A Mountain is a portion of the land raised considerably above 
the surrounding portion, as Mont Blanc, Snoiodon. When under 
2,000 feet above the level of the sea, they are termed hills, as Cots^uold 
Mills, Malvern Hills. When they form a continuous line they 
are called chains, or ranges, a series of which are termed a system. 

A Volcano is a mountain which casts forth smoke, flame, lava, 
ashes, &c., as Vesuvius, in Italy. 

A Valley is a hollow, or lowland, lying between mountains and 
hills ; when very narrow at the bottom, with steep sides, it is called 
a ravine. 

A Plain is a portion of country nearly flat, or level, and not 
raised much above the level of the sea. When a tract of thisr 
description lies high, it is called a 'plateau or tableland. A series 
of plains at dififerent levels are called terraces. 

Plains have received specific names in difierent parts of the world, 
derived from the languages of the people. Thus, in North America 
they are called savannas or prairies (meadows) ; pampas, llanos, 
and selvas, in South America ; steppes, in the south-east of 
Europe and the north-west of Asia. Zandes is the name given to 
extensive marshy or sandy tracts, covered with heath, on the coast 
of the Bay of Biscay. 

A Desert is a barren tract of country, usually consisting of sand 
and rocks, as the Sahara Desert. A fertile spot in the midst of a 
desert country, caused by the presence of water, is called an oasis. 

The Ocean is the continuous mass of salt water which surrounds 
the globe, particular parts receiving particular names, as the 
Pacific Ocean (peaceable). 

A Sea is a smaller body of salt water nearly surrounded by land, 
as the Mediterranean and Baltic Seas. 

A Gulf is a portion of the sea running into the land and having a 
narrow opening, as the Gulf of Mexico. 

A Bay is a portion of the sea running into the land, having a wider 
opening than a gulf, as the Bay of Bengal. 

A Creek is a small inlet on a low coast. In Australia and 
America it means a small inland river. 

A Channel is a body of water uniting two larger bodies of water. 
When it is narrow it is called a strait or sound. 

A Lake is generally fresh water surrounded by land, as Lake 
Superior; but some are salt, and when large are called seas, as the 
Caspian Sea. 

A Lagoon is a shallow lake formed on low lands by the overflow- 
ing of rivers or seas. 

A KiVER is a stream of fresh water rising in the land, draining a 
portion of the country, and flowing into the sea, a lake, or another 



70 PHYSIOGRAPHY. 

river. A small stream is termed a rivulet or Irook. A river that 
falls into another is called a tributary, and where they meet the con- 
fluence ; the place where the river rises its source, and where it 
empties itself into the sea its mouth, but when very wide it is termed 
an estuary, firth, or fiord. The channel which contains its waters is 
the bed and the sides its hanks. 

The Basin of a river is that portion of country drained by the 
river and its tributaries. All the basins inclined to any particular 
sea are called a river system. 

A Waterparting is the elevated land which separates one river 
basin from another. 

A Delta is a tract of alluvial land deposited at the mouths of 
certain rivers, dividing them into two or more streams, so called 
from its resemblance to the Greek letter A, named delta. 

EXTENT AND DISTRIBUTION OF LAND AND 
WATER. 

66. Land and Water are distributed very unequally, as only 
a little more than one-fourth is land, the remaining part, nearly 
three-fourths, being water ; or, more exactly, out of 197 millions of 
square miles 51^ are land and 145J water — that is about 26*2 per 
cent land and 73 "8 per cent water, its general distribution being as 
tollows : — 

Northern Hemisphere ... | ^^f ' H^ ) 

Land, 13 > milhon squaxe miles. 
Southern Hemisphere ... | ^^^^^;^ g^^ ^ 

Total 197 

Of the land there is about three times as much in the Northern 
Hemisphere as there is in the Southern, and in the Eastern about two- 
and-a-half times that in the Western. Regarding the distribution 
in the zones it may be stated that in the North Frigid Zone about 
one-third is land, in the North Temperate about one-half, in the 
Torrid Zone one-half, and in the South Temperate one-tenth. 

Dividing the globe into two hemispheres, one having London* for 
its centre, and the other New Zealand, the former will embrace -^f of 
the whole land, and the latter only jV land, or nearly all water. 
This fact may account for the prosperity of London, being placed as 
it were in the very centre of the nations. 

67. Divisions of tlie Water. — There is but one ocean really, 
but for the sake of convenience it is divided into five different parts, 
or basins, namely — 

* Tlie exact spot lies in the George's Channel, near the middle. 



PHYSIOGRAPHY. 71 

The Atlantic Ocean, between the western coasts of the Old 
World and the eastern coasts of the New. 

The Pacific Ocean, between the eastern coasts of the Old World 
and the western coasts of the New. 

The Indian Ocean, south of Asia and east of Africa. 
The Arctic Ocean, lying round the North Pole. 
The Antarctic Ocean, lying round the South Pole. 
The areas of these divisions are roughly estimated as follows : — 
Greatest Length. Greatest Breadth. Areas. 

Miles. Miles. Square Miles. 

Pacific Ocean 9,000 12,000 72,000,«-00 

A.tlantic Ocean 9,000 4,100 35,000,000 

Indian Ocean 4,500 4,500 25,000,000 

^ctic Ocean 3,240 2,500 5,000,000 

Antarctic Ocean ...3,266 3,266 5,000,000 

68. Area and Distribution of the Land.— As before stated, 

there are about 51^ million square miles of land out of the total 
197 million square miles area of the earth. Dividing the land into 
four divisions — namely, Europe, Asia (with Polynesia), and Africa, in 
the Eastern Hemisphere, commonly known as the Old World, and 
America (North and South), known as the New World — ^the respective 
areas are as follow : — 

OLD WORLD, including ISLANDS. 

Square Miles. Relative Size. 

Europe 3,500,000 1 

Asia, with Polynesia ...21,500,000 6 

Africa 12,000,000 3f 

NEW WORLD, including ISLANDS. 

North America 7,500,000 2f 

South America 7,000,000 2 

Taking Australia by itself it contains about 3| milHon square 
miles, and the islands surrounding about 1 million ; so that Oceania 
contains 4 J millions of square miles. It is calculated that the area of 
all the islands on the globe (not including Australia) is between 2 J and 
3 millions of square miles. 

Islands are divided generally into three classes : (1) Continental^ 
or seaward extensions of the continent upon whose coast they he, as 
the British Isles, for instance, which evidently belong to the same 
formation as the continent of Europe, and have, at some period, been 
attached to it, proofs of which are shown in the fossils of animals 
belonging to Europe having been found in this country ; and the 
only way to account for their presence here is that they must have 
walked over ; but since that time the land on which the German 
Ocean now stands has sunk to a depth of — in the deepest part — 
50 fathoms, so that an elevation equal to that would again connect 



i 3 PHYSIOGRAPHY. 

them. (2) Volcanic islands, which are generally of a different 
structure to the continent near them. The chief of this class are 
the Sandwich Islands, Marquesas and Society Islands, in the Pacific, 
Iceland, Jan Mayzen Island, the Azores, the Canaries, Cape de 
Verdes, St. Helena, Ascension, Trinidad, &c. (See " Volcanoes," 53 
and 54.) (3) Coral islands, or those formed by the coral polyps. 
(See "Organically-formed Kocks," 47 and 56.) The chief of these 
occur in Polynesia, the West Indies, the Eed Sea, the Indian Ocean, 
and the Atlantic Ocean. The largest barrier-reef, off the north-east 
of Australia, is more than 1,000 miles in length. 

Among the largest of the islands may be mentioned Greenland, 
containing 380,000 square miles ; Borneo, 280,000 ; New Guinea, 
274,500 ; Madagasgar, 234,000 ; Sumatra, 177,000 ; Niphon, 109,000 ; 
and Great Britain, 83,830. 

69. Configuration (Shape) of the Land.— Regarding the 

general aspect of the surface of the land there are two things to be 
considered — (1) Its horizontal outline, giving us the contour ; and 
(2) its vertical outline, or projile. Considering the horizontal outline 
of the different masses, they present many points of resemblance and 
certain points of contrast. 

(a) Though the greater bulk of land lies in the Northern Hemi- 
sphere, the greatest extension of the Old World is from east to west, 
while that in the New is from north to south. Hence the latter is 
subject to a greater diversity of temperature, and also of vegetable 
and animal life, owing to its crossing the different zones — frigid, 
temperate, and torrid. 

(6) Both masses in the Old and the New World attain their greatest 
dimensions from east to west, along the same parallel of latitude, 
namely, that of 50° north, which places much of North America, 
Europe, and Asia within the temperate zone, while only the narrower 
portions of South America, Africa, and the East India Islands lie 
under the intense heat of the equator. 

(c) Both the Old and New Worlds present a broad base towards 
the north, terminating along the parallel of 72°, and taper towards 
the south, terminating in far separated promontories. The direction 
of the chief peninsulas in both worlds (Old and New) is towards the 
south, these peninsulas being, in many cases, accompanied by an 
outlying island or islands, as South America by Tierra del Fuego and 
the Falkland Islands, Africa by Madagascar, Hindostan by Ceylon, 
and Australia by Tasmania. It may also be noticed at the same 
time that these promontories terminate in abrupt rocky precipices, 
which are often the termination of a mountain range. 

(d) In each hemisphere (Western and Eastern) a large portion is 
nearly entirely separated from the principal mass, Africa being 
aearly separated from the Old World, and the severance of Australia 



PHYSIOGRAPHY. 73 

from Asia ; while in the New, South America is very nearly separated 
from Korth America. 

(e) The general disposition of the continents and larger islands is 
in the direction of their principal mountain axes, or mountain 
ranges. The tendency of islands is generally to arrange themselves 
in groups, or archipelagos. 

(/) The extremities of each continent (Old and New World), north 
and south, are nearly in the same meridian — the north-west point 
of Greenland being nearly in the same meridian with Cape Horn, 
North Cape Vvith the Cape of Good Hope, &c. 

70. Coast-lines. — The shape of the coast-lines presents also 
some peculiar features on opposite sides of the same ocean, 
projections or protuberances on one side corresponding with recesses 
on the other. This may be noticed very strikingly with regard to 
the Atlantic, where the recesses in the New World seem made for the 
protuberances of the Old to fit exactly in. 

The extent of the coast-line is one of the most important features 
in Physical Geography, as on it depends greater diversity of climate 
and productions, and the facihties for navigation and commerce, from 
which nations derive their wealth, power, and independence. This 
may be regarded as the chief cause of the greatness of Europe and 
North America, as they have the greatest relative extent of coast-line. 
Africa on the contrary, has the least relative coast-line, and is the most 
uncivilised, the country being in a great degree shut out from the 
influence and enterprise of commerce, and the benefits resulting 
therefrom. The following table shows the relative extent of coast- 
line of the difierent continents : — 

^ .V „- Sq. miles 

Sq. miles. ^-^1°' ^^--^ 

Europe 3,500,000 20,000 17o' 

Asia 17,500,000 33,000 533 

Africa 12,000,000 16,500 680 

North America 7,500,000 28,000 260 

South America 7,000,000 16,500 420 

Australia 3,500,000 7,600 460 

From the above it will be seen that Europe has one mile of coast 
for every 170 square miles of surface, and North America one mile 
for every 260 square miles of surface, but Africa only one mile for 
every 680 square miles of surface. It has hardly an inlet where a 
ship can harbour in round the entire coast, but in Europe there are 
gulfs, inland seas, and peninsulas, the latter being in places again 
divided into inlets, &c. 

71. Vertical Outline. — ^The surface of the land is very varied, 
aasuming many forms and elevations. In all the continents there is 



74 PHYSIOGEAPHT. 

a gradual nse rrom the seashore towards certain points or ridges in 
the interior, which form the great loaterpartings of their respective 
continents. (There are one or two exceptions to this rule, namely, 
the region surrounding the Caspian Sea, Dead Sea, and Lake Ural.) 
This ridge of greatest elevation is placed more towards one side 
than the other, so that there are two slopes of unequal length, the 
long side, which is generally four or five times the length of the 
other, forming the slope, and the shorter, the counter-slope. The long 
slopes in the Old World are turned towards the north, and the short 
ones towards the south. But in the New World the long {or gentle) 
slope is turned towards the east, and the short (or rapid) one towards 
the west. 

According to Hughes, the lengths of the longer and shorter slopes 
are : — 

North Slope. South Slope. 

Eastern Asia 2,600 400 

Western Asia 900 80 

Central Europe 450 100 

Africa ,.o..... 3,300 600 

East Slope. West Slope. 

Korth America 1,600 800 

Central America 2,000 300 

South America 1,850 50 

In all continents the elevations increase from the poles to the tropics ; 
and also extend in the line of the greatest length of the continents. 
Thus the highest point in the Old World — namely. Mount Everest — is 
situated near the Tropic of Cancer, and that in the New World 
(Aconcagua in Chili) is not far south of the Tropic of Capricorn. 
The effect of this law is to temper the fierceness of the heat of the 
tropics, giving them a variety of climate. 

Mean Elevation. — The mean elevation of a continent is the height 
above the sea level that it would he if all the hills and mountains were 
levelled, filling all the valleys up, so that the tuhole shoidd have an even 
surface. It has been estimated that the mean elevation of Europe 
would be 670 feet ; of Asia, 1,132 feet ; of Africa, 910 feet ; of North 
America, 750 feet ; of South America, 1,150 feet. 

MOUNTAINS. 
72. It is seldom that a moTintain occurs singly. They 

appear mostly in ranges or chains. There are a few instances where 
they do, owing their origin chiefly to volcanic energy, among which 
may be mentioned Mount Egmont in New Zealand, and the Peak of 
Teneriffe in the Canary Islands. The chains or ranges generally 
consist of parallel ridges, the centre one being the highest. They 



PHTSIOGR&.PHT. 75 

have generally their highest elevation near the middle, gradually 
drooping down into the plain towards their extremities. The lateral 
ridges which break off from these may again, in their turn, send o£E 
smaller ridges or spurs in numerous ramifications. Several chains 
constitute what is called a group, and several groups a system. 

The outlines of mountains depend chiefly on the geological struc- 
ture, and partly on the amount of waste and degradation to which 
they have been subjected. In this aanner, hills that are com- 
posed of hard basalts and greenstones, alternating with soft tufas or 
stratified rocks, assume tenaciform declivities ; and extinct volcanic 
hnis put on a crateriform aspect. Those chiefly composed of hard 
massive strata — as limestone, conglomerates, and sandstone — present 
a tabular appearance ; and mountains capped and flanked by crystal- 
line schists and quartz are serrated with peaks and pinnacles. 

The mountain chains often traverse immense regions, forming the 
boundaries of great nations living round their base. For instance, 
the Andes, continued by the Mexican and Rocky Mountains, extend 
through all the different zones and climates of the world. 

73. Mountain Systems. — There are really only two great 
mountain systems in the world. (1) That in the New World is a 
continuity of a vast and extremely precipitous line of very elevated 
mountains running parallel with the west coast of America, and from 
the Arctic Ocean almost to the extremity of Patagonia — a distance 
of nearly 9,000 miles. Throughout the whole of this border we notice 
a distinct and unmistakable tendency to a system of double or triple 
ridges, nearly or exactly parallel, extending for hundreds of miles in 
succession, and resumed again and again when interrupted. (2) In 
the Old World there is a broad belt of mountainous country running 
through the land in a general direction from the East Cape, in 
Siberia, west-south-west across Asia to Spain and Morocco, being a 
distance of between 8,000 and 9,000 miles. AU mountain chains, with 
the exception of the African and Australian ranges, are offshoots of 
one or the other of these two systems. 

For the sake of reference the mountains have been arranged in 
various systems. Thus, those of Europe are arranged into the 
BHtannic, Iberian (or Spanish), Alpine, Carpathians, Scandinavian, 
Uralian systems, &c. Those of Asia into the Taurus, Kuen-lun^ 
Thian-shan, Altai, Himalayas, &c. Ai'rica, into the Atlas, Abyssinian, 
Eastern, Western, or Guinea, &c. While those of the New World are 
the HocJcy Mountains, the Mexican Andes, and the Cordillera of the 
Andes. 

74. Europe. — The Britannic System consists of a number of 
detached chains, as the Grampians, Cheviots, Cumbrian, Hibernian, 
and Welsh mountains ; they are sometimes said to form the southern 
continuation of the Scandinavian system. The highest mountains 



76 PHYSIOGRAPHY. 

are Ben Nevis, 4,406 feet, in Inverness- shire, and Caimtoul, in Aber- 
deenshire, 4,285 feet ; the highest in England and Wales is Snowdon, 
3,590 feet ; and in Ireland, Carn-Tual, 3,412 feet high. 

The Spanish System embraces several detached mountain chains, 
including the Pyrenees, the Cantabrian Mountains, the Sierra 
Nevada, the Sierra Morena, and the sierras of the central tableland. 
The reason of their being called sierras is on account of their jagged 
and sawlike appearance, Thenamecomes from a Spanish word meaning 
a saw. The principal chain is the Sierra Nevada, ranging from east to 
west, the highest point is Mulhagen, 11,678 feet, and Maladetta, in 
the Pyrenees, 11,168 feet. The Sierra Morena runs parallel with the 
Nevada chain, but lies farther north. There are several minor 
chains lying between the Pyrenees and the Sierra Nevada. 

The French System includes all the hilly eminences in France 
lying to the north of the Garonne, west of the Rhone and south of 
the Rhine. The chief detached mountains are the Auvergne 
Mountains, which are a group of extinct volcanoes, the highest peak 
of which is Plomb de Cantal, 6,113 feet. 

The Alpine System embraces the whole of those extensive and 
lofty mountains which, from Switzerland as a centre, spread in ranges 
more or less persistent, which confer on Southern Europe one of its 
chief and peculiar features. It may also be said to form the back- 
bone of the continent. These ranges have many minor divisions, as 
the Maritime, Cottian, Graian, Pennine, Bernese, Carnic, Noric, and 
other Alps, which extend in a north-east direction from the shores 
of the Mediterranean to the tableland of Bohemia ; the Apennines, 
traversing the entire length of Italy, and terminating in the volcano 
Etna, in Sicily ; the Slavo-Hellenic ranges, lying between the shores 
of the Adriatic and the plains of the Danube ; and the Balkan 
group, in Turkey, ranging from east to west. The highest point in 
this system is Mont Blanc, 15,744 feet. The other chief heights are 
Mont Pelvoux, 14,108 feet ; Etna, in the Apennines, 10,874 feet ; 
Tehan-Dagh, 9,700 feet, in the Balkan mountains ; Olympus, 9,749 
feet, in the Hellenic range. 

The Carpathian System includes all the mountains and eminences 
situated between the Rhine, Dneiper, and Danube, the plains of 
Northern Germany and Western Poland. The western portion of 
the Carpathian chain, near the mouth of the Danube, is called the 
Transylvanian range. The highest point in this range is Ruska 
Joyana, 9,912 feet, in the Eastern Carpathians. In the main range 
there are several high peaks grouped upon one very large mountain, 
Tatra, the highest point being 8,524 feet ; the Csalic Peak, 8,314 
feet ; and the Lomnitz to more than 8,000 feet. 

The Scandinavian System embraces the whole of the mountains 
and highlands of Norway and Sweden, extending in a north-eastern 
direction from the Naze to the North Cape — a distance of nearl?- 



PHYSIOGRAPHY. 77 

1,000 miles. Tliey consist of the Novrska Fjellen (Norwegian range) 
and the Kjoien. The latter lies to the north, being ahout 500 mUes 
in length, but not so generally elevated as the former, though it 
rises to about 6,200 feet in Sulitelma. The former is about 400 
miles long, lying to the south, and containing the highest points in 
the group, viz., Sneehatten, in the Dovrefeld (in the middle), about 
8,000 feet ; though in the southern range Skegstol-tend is said to 
be 8,670 feet. 

The Ural System or chain forms the boundary line between Europe 
and Asia, embracing the Ural Mountains and forming the water- 
parting between the extensive basins of the Volga and Obi, This range 
runs in a true meridianal direction for a distance of more than 1,600 
miles, and consists of round-backed, plateau-shaped masses, of very 
moderate height, in most places not exceeding 2,000 feet, though 
there are one or two points a little over 5,000 feet, viz., Koujak-Ofski, 
5,397 feet, and Obdorsk, 5,286 feet. 

75. Asia. — The Altai, the great mountain system of the Old 
World, commences on the shores of Behring Strait, at the East 
Cape, ranging for some distance to the west. Afterwards it bends 
toward the south, branching into Kamtschatka. The chief range 
bends again to the west, running through Siberia, when it is called 
the Aldan Mountains, still continuing westward along the 50th 
parallel of latitude, passing Lake Baikal, and reaching the 84th degree 
of longitude. The breadth of this range in many places exceeds 800 
miles, but the height is not so great in comparison to its length 
and breadth. The highest point is Bielukha, 12,796 feet. Partly 
parallel to the Altai range are three ranges, viz., (1) Thian-shany 
(2) Kuen-lun, and (3) the Great Himalaya range. The first two 
run eastward, Thian-shan near to the 42nd parallel of latitude, 
and Kuen-lun near to the 36th, into China. The last named forms 
the southern boundary of the desert of Gohi, Thian-shan lying to the 
north of that desert. The highest point in the Thian-shan is Khan- 
Tengri, 21,000 feet. In the Kuen-lun some points reach the height of 
22,000 feet. In these chains are active volcanoes, some as far as 
1,500 miles from the sea. The last of these three ranges — namely, 
the Great Himalaya — extends about 1,500 miles along the southern 
border of the central plateau, separating Thibet from Hindostan. 
The highest point is Mount Everest, reaching 29,002 feet, or more 
than 5| miles in height, being the highest peak in the world. There 
are several other very high summits in the central portion, attaining 
in several places the height of about 25,000 feet, and between 30 
and 40 more than 23,000 feet. Kinchingunga reaches 88,156 feet, 
and Dhawalagiri 26,826 feet. The passes of the Himalaya are from 
10,000 to 17,000 feet high. It has been noted that vegetation 
ascends higher on the north side than on the south side. This 
singular fact is supposed to arise from the reflection of the sun's 



78 PHYSIOGRAPHY. 

The Hindoo Cooch (or Koosh) traverse the north of Afghanistan 
and Persia. They may be regarded as prolongations of the Himalaya. 
The highest peak exceeds 20,000 feet. The Taurus and Anti-Taurus 
ranges, which encircle the tableland of Asiatic Turkey, the highest 
point of which is Mount Argish (or Argons) in Armenia, 13,197 feet. 
In connection with the Taurus may be mentioned the Lebanon 
range, which attains a height of 10,050 feet in Dahr-el-Khotib ; 
Hermon, 9,376 feet ; and Sinai and Horeb, 7,413 and 8,593 feet 
respectively. 

The Caucasian includes the mountains of Elburz and those 
between the Caspian and Black Seas, whose highest points are Dema- 
vend, 21,500 feet ; Elburz, 18,493 ; Koschtantan, 17,096 ; Dychtan, 
16,925 ; and several others exceed 16,000 feet in height. There are 
several smaller ranges that have not been noticed, the chief of 
which are the Armenian Mountains, ranging between Turkey and 
Persia, the highest peak being Mount Ararat, 17,112 feet. 

76. Africa. — In the extreme north we have the Atlas System — 
between the Mediterranean seaboard and the Sahara —extending 
from Tripoli on the east, to the Atlantic on the west, namely, to 
Cape Geer. Geologically, it is connected with the systems of 
Southern Europe, and consists of three or four parallel ranges, 
gradually increasing in height from east to west. At Tripoli it is 
only about 2,000 feet above the level of the sea, in Tunis it is 4,500 
feet, in Algeria 7,700, while in Alorocco it rises to the height of 
11,400 (Mount Miltsin or Atlas) and Jebel Tedla to 13,000 feet. 
Several smaller ranges proceed from the main range — one branch 
travelling north and terminating in Cape Spartel, at the Strait of 
Gibraltar. 

The next system of importance is the Abyssinian, which is con- 
nected with and forms the lofty tableland of Amhara, the height 
of which is 8,000 feet above the level of the sea. The two principal 
chains — namely, Samen and Taranta — range in a northerly direction, 
between the upper forks of the Nile and the Eed Sea, and run 
along the latter' s shores as far as the lower hills of Egypt. In the 
Samen, or upper range, we have the highest points, namely, Eas 
Detchen, 15,986 feet ; Buahat, 15,000 feet ; Abba Jaret, 14,707 
feet. In the Taranta, or lower range, the heights descend gradually 
from 9,000 to 5,000 feet, towards the Red Sea and Plains of Egypt. 
This system consists chiefly of granites, porphyries, syenites, and 
crystalline schists. 

The Guinea System usually embraces the Kong and Cameroon 
Mountains. The Kong, between the Gulf of Guinea and the Niger, 
generally average from 1,000 to 3,000 feet ; and the latter, on the 
west, stretching eastward, rise to aljove 13,000 feet in height. The 
hills of Cape Colony form a series of sandstone plateaux, or karoosg 



PHYSIOGRAPHY. 79 

rising from Table Mountain, 3,816 feet, to the sutotnits of Nieuvelt 
and Snieuvelt Mountains, in the north of the colony, which in some 
cases reach 10,000 feet, as in the Compass Bay, in the Sneeuwveld 
or Snowy Range. This system of mountains is sometimes termed the 
Cape System. 

Polynesian System. — Not much is at present known of the moun- 
tain chains of Austraha. The highest points in this country are 
Mount Kosciusko, 6,500 feet, and Sea View, 6,000 feet. These are 
in the chain which extends along the eastern coast, from Torres 
Strait on the north, to the extreme point of Tasmania on the south. 
The highest points in Polynesia are the active volcanoes of Manna 
Kea and Manna Loa, in Hawaii, each about 14,000 feet, though in. 
New Zealand there are some points reaching from 10,000 to 12,000 
feet. 

The highest mountains of the Old World are formed of granite ; 
and gneiss and mica-slate also form large mountain masses. 

NEW WORLD, OR AMERICAN SYSTEMS. 

77, South America. — The mountain chains of South America 
may be ranged into two systems. (1) The Cordillera of the Andes; 
and (2) The Mountains of Brazil. The Andes extend along the 
western coast, from the Magellan Straits to the Caribbean Sea, in 
two or three parallel chains, a distance of nearly 4,500 miles, and 
varying in breadth from 40 to 340 miles. They may be termed the 
largest mountains in the world, being so lofty throughout, and 
differing from the Himalaya by rising from the sea. The highest 
points are in the Bolivian Andes, reaching in many places from 
13,000 to over 21,000 feet. In Chili many summits exceed 16,000 
feet ; the highest peak of the range — namely, Aconcagua — being 
22,300 feet. Chimborazo is 21,424 feet. In Patagonia they do not 
exceed much above 6,000 feet. This system (Andes) forms one of 
the grandest centres of volcanoes in the world, most of its highest 
peaks being volcanic — Aconcagua, for instance, the highest of the 
range. 

78. North and Central America.— The Andes also form the 

chief system of Central and North America, though known by a 
different name than in the South. Continuing from the Isthmus of 
Panama to the North of Mexico they are called Central Andes. The 
greater part of Mexico consists of magnificent tablelands, from 5,000 
to 8,000 feet high. The highest peak is Popocatapetl, 17,720 feet. 
In North America the system is termed the Rocky Mountains, 
which consist chiefly of two parallel ranges, running generally in 
the direction of the Pacific to the Arctic Ocean, a distance of more 
than 5,000 miles, so that the Andes extend a total distance of 



80 PHYSIOGRAPHY. 

nearly 10,000 miles, and in places they are 1,000 miles in breadth. 
The highest peaks of the Rocky Mountains are Mount Brown, 16,000 
feet, Mount Hooker, 15,000 feet, and Mount Murchison, 15,000 feet. 
The summits of the Andes are formed of porphyry and basalt 
(igneous rocks). In the maritime or western range the highest peak 
of ITorth America is to be found, namely, Mount St. Elias, on the 
coast, in latitude 61°, reaching a height of 17,800 feet. On the east 
are the AUeghanies, or Appalachian Mountains, extending for about 
1,200 miles in length, the highest point of which is Mount Wash- 
ington, 6,634 feet. 

TABLELANDS, OK PLATEAUX. 

79. Tablelands are extensive upland plains, consisting of very 
large areas of surface, high above the level of the sea, and varied by 
hill and dale, lake and river. Few mountains have their bases at or 
near the sea level, but mostly rise on these tablelands. It is from 
these tablelands that many of our noblest rivers have their sources. 
The chief tablelands are — 

Asia. — It is in this continent that we have the grandest examples 
of tablelands and plateaux, both in extent and elevation, occupying 
two-fifths of the entire continent, stretching from the Mediterranean 
to the Pacific, being 6,000 miles in length, 2,000 miles broad at the 
eastern extremity, 700 to 1,000 in the middle, but narrower towards 
the Mediterranean. We may divide these plateaux into two great 
divisions, namely, (1) The Central Asia or Eastern Plateaux ; (2) The 
Western Plateaux, joined to the Eastern by the Hindoo Cooch. In 
the Central Plateaux lie the vast deserts of Gobi, Scha-mo, and 
Hanai (Dry Sea). The rainless desert of Gobi covers an area of 
400,000 square miles, rising from 4,000 to 6,000 feet in height. To 
the south of these lie the plateaux of Thibet, the loftiest inhabited 
portion of the globe, having an elevation (between the Kuen-lun and 
the Himalaya) of 15,000 feet, and reaching in some points 17,000 
feet, with an area of 166,000 square miles To tne south-west of 
the Central Plateaux lie the great tablelands of Persia, or Iran, rising 
from 2,300 to 3,500 feet above the sea level, and with an area of 
300,000 square miles, presenting a riverless and desolate region. In 
succession to this plateaux extend the tablelands of Arabia and the 
Great Desert of Sahara, in Africa. The entire sandy and arid table- 
lands of Asia — namely those of the central and western plateaux — 
extend over 120° of longitude and 17° of latitude, or an area of 
6,000,000 square miles Not belonging to either of the above 
divisions are the plateaux of Armenia, north-east of Turkey in Asia, 
7,000 feet high, and the Deccan, in the Indian Peninsula, rising 
from 1,600 to 2,000 feet in Hyderabad, and 4,000 feet and upwards 
in Mysore. 



PHYSIOGEAPHY. 81 

Europe. — The plateaux of tliis country are very few, and of little 
importance. The highest are those of Spain, ranging from 2,000 to 
3,000 feet above the sea, and extending into Portugal, covericg an area 
of 100,000 square miles. The central part is edged or fringed by 
mountains on all sides, and the ranges of the Sierras Nevada, 
Morena, &c., rise out of it. The largest plateau in extent hes in 
the east of Europe, separating the low plains of Northern and Central 
Eussia ; its area is more than 150,000 square miles. To the south 
of this plateau lies the Carpathian, but not near so large. 

Africa. — Not much is known of the tablelands of Africa; but 
some elevated tracts occur in Abyssinia, extending southwards to 
the extremity of the continent. The great lakes, Albert Nyanza 
and Victoria Nyanza, are situated on this tableland. Some parts of 
Africa lie really below the sea level. 

North and South America. — In Mexico, or Central America, 
we find the greatest unbroken extent of tableland known, extend- 
ing, north and south, a distance of 1,600 miles, and a breadth of 360 
miles, or more. The surface is a dead level, with the exception of 
where volcanic cones rise up, and ranges from 4,000 to 7,000 feet in 
height. 

In North America the chief plateau is called the Great Basin, 
lying between the ranges of the Sierra Nevada and the Rocky 
Mountains, and extending from Mexico to the Arctic Sea, about 
2,000 miles, its greatest breadth being 600 miles, and mean height 
5,000 feet. Another tableland, but not so large, stretches from 
Hudson Strait, in Labrador, to the north of Alhambra, its greatest 
height not exceeding 2,000 feet. In South America the principa* 
one is Desaguadero, lying high up among the tops of the Andes, 
attaining in Bolivia a height of 13,000 feet, its length being about 
500 miles, and breadth from 80 to 60 miles. It is on this plain 
that Lake Titicaca stands, at an elevation of 13,000 feet, being 
one of the most elevated sheets of water. The Plateau of Quito 
is 200 miles long and 30 wide. The city of Quito is situated at the 
height of 9,540 feet, having a view of eleven snow- clad mountains 
(nevadoes). The only other plateau worthy of note is the Plateau 
of Brazil, the area of which is about 1,500,000 square miles, and the 
mean height about 3,000 feet. 

The following table gives a few of the most elevated tablelands, 
compiled principally by Humboldt : — 

Feet. 

Bavaria, Germany 1,660 

CastiUe, Spain 2,240 

Plateau of Switzerland 2,000 

Victoria Nyanza, East Africa 3,300 

Iran, Persia 4,500 

F 



82 PHYSIOGRAPHY. 

Feet. 

Armenia, South of the Black Sea 7.000 

Mexico, Central America 7,483 

Quito, Andes 9,600 

Bolivia, Andes , 12,900 

Thibet 10,000 to 15,000 

Desaguadero, Andes 13,000 

Ravanabradu, East Asia 15,000 

LOWLAND PLAINS OR DESERTS. 

80, In the Old World the principal plain is known as the 
Great Northern Plain, which stretches in length from the German 
Ocean (shores of Holland) through Prussia, Poland, Russia, and 
Siberia to Behring Strait, only interrupted by the transverse range 
of the Urals ; and in breadth from the shores of the Arctic Ocean, 
nearly to the base of the Carpathians, in Europe, and to the table- 
land of Iran (Persia) and edges of the Altai Mountains, in Asia ; and 
altogether it extends over 190° of longitude, including an area of 
more than 5,000,000 square miles, being nearly one-third of the 
area of Asia and Europe, The part in Europe is divided into the 
Germanic Plain, in the west, and the Sarmatian Plain, in the east ; 
while in Asia we have the steppes of Kirghis, I shim, and Baraba, in 
the south-west, and the Siberian Plain in the north-east. 

In the Germanic Section occur the low-lying polders and morasses 
of Holland and the sandy tracts between the rivers Elbe and 
Weser, which are interspersed with heaths, marshes, &c. The 
Sarmatian Section extends from the Baltic to the Black and 
Caspian Seas and the Ural Mountains, the only interruption being 
the Valdai Mountains, It may be said to consist in the northern 
division of cold, swampy, and partially-wooded flats, much of it 
consisting of marsh land, and large tracts covered by peat, called 
trunda. The middle division differs much from the northern, being 
mild in climate, fertile, its surface undulating, richly wooded, and 
well watered. This is the pleasantest part of Russia. The southern 
division consists of steppes and river swamps, impregnated in many 
places with saline matter. Towards the eastern extremity the plain 
assumes the character of the steppes of Kirghis, Ishim, and Baraba. 

S'eppes, as their name implies, are wide, treeless, monotonous 
deserts, covered with long coarse grass and shrubs during a brief 
summer, and in the winter converted into bleak wastes. These 
steppes are estimated to cover an area of one million square miles. 

Landes, or heaths, are those extensive areas of sand-drift which 
stretch southward from the mouth of the Garonne, on the coast of 
the Bay of Biscay. They are sometimes marshy, but mostly covered 
with d^rarf shrubs (sea pine) and heath. . 



PHYSIOGRAPHY. 83 

Polders are flat tracts of land in Holland, reclaimed from the sea 
and protected by dyJces or embankments. 

Dunes are hillocks of drift-sands, as those which stretch along the 
coast of the Netherlands and North of France. The minor ones of 
Europe are the plains of Lombardy, watered by the Po, and those of 
the Middle and Lower Danube. 

Among the other secondary plains of the Old World may be noticed 
the Plain of China, occupying 200,000 square miles ; the plains of 
Hindostan, extending from the base of the Himalayas to the Deccan, 
and from the Ganges to the Indus (this plain is often inundated in 
its lowest parts during the rainy season); the plain of Turan 
(1,000,000 square miles), extending along the southern shores of 
Lake Aral to the Caspian Sea ; and the plains of Mesopotamia 
(165,000 square miles), in Western Asia, between the Euphrates and 
the Tigris. In Africa, the Desert of Sahara, which has been till 
of late considered a depressed plain, consists of an elevated plain, the 
mean height of which is about 1,000 feet. 

New "World. — Between the Rocky Mountains and the Alleghany 
Mountains, in North America, from the Arctic Ocean, is one very 
large central plain, watered at the lower part by the Mississippi and 
its tributaries, and containing some of the largest fresh- water lakes 
known. This plain may be said to extend to the most southern 
part of America — Tierra del Fuego — the only interruptions being in 
the case of the Gulf of Mexico and the Caribbean Sea. Its different 
portions are called prairies,* or savannas.t In the Southern Con- 
traent it is situated between the Andes and the Cordilleras of Brazil. 
The entire length of this one plain is about 9,000 miles. 

The Atlantic Plain lies between the Alleghanies and the Atlantic 
Ocean, from the Gulf of Mexico to Massachusetts. 

The Central Plain of South America is divided into three well- 
marked river plains — viz., those of the Amazon, Orinoco, and La Plata — 
termed respectively selvas, llanos, and pampas. The first {selvas) 
comprise the largest river basin of the world (1,500,000 square miles), 
covered by an immense forest, presenting the rankest luxuriance of 
forest growth, which in many places is so tangled with the under- 
wood, &c,, that it can only be penetrated by the river courses. The 
llanos, or grassy flats, occupy an area of 160,000 square miles, and 
form the lowest and most level tracts in the world, not varying a 
single foot for hundreds of mUes. In the wet season these are 
inundated, and a rich alluvial deposit is formed, which, after the 
subsidence of the water, is quickly covered with verdure, so that 
the natives term it the Sea of Grass; but it does not last long, as 
the droughts which follow soon cause it to become parched and to 
wither away. The pampas comprise the basins of the Parana, La 

* Prairie, an extensive meadow. + Savanna, a bed-sheet or meado- 



84 PHYSIOGRAPHY. 

Plata, Uruguay, &c., and cover an area of about 880,000 squaro 
miles. They consist of rich alluvial soil, generally covered with tall 
grasses, thistles (some 10ft. high), weeds, &c., though in some places 
they are saline and barren. The desert terrace land of Patagonia, 
stretching 800 miles from Rio Colorado to the very end of the 
continent, is a sterile country, consisting of shingle, strewn with 
boulders, &c. With its fierce hurricanes, hot winds, and chilling 
blasts, it is one of the most desolate regions on the globe. 

Valleys are of several kinds. Some are valleys of erosion, having 
been caused by the intermittent action of running water wearing 
away and carrying off the fragments of rock, forming deep and 
narrow ravines, which gradually widen into a valley ; others, 
according to the theory of depression and emergences, would owe 
their origin to some part having been raised or other parts depressed ; 
and others would be caused by the mountain torrent, which receives 
the product of the springs, snows thawed, rains, &c. 

Canons are narrow channels cut out by the rivers themselves, the 
water occupying the bottom from side to side, an example of which 
is the river Colorado, rising in the Rocky Mountains. The Grand 
Canon of this river is 240 miles long and from 2,000 to 4,000 feet 
deep. 

THE OCEAN. 

The waters of the globe, as previously stated, cover about 145^ 
millions of square miles, which all over the earth follow the well- 
known law of fluids, namely, that of assuming a uniform or 
natural level at a nearly equal distance from the centre of the 
earth. Though the ocean has different names in different parts of 
the world, yet, in reahty, there is but one ocean. Its form and . 
various divisions can be best learned by inspecting a map of the world, 
going over it several times until quite familiar with every arm, or 
inland sea. The ocean is one of the greatest modifiers of the 
climate. (See " Climate.") 

81. Density of the Oceans. — Sea water has a greater density 
than fresh water, varying with the amount of salts dissolved in it. 
A cubic foot of fresh water weighs 1,000 ounces, but the same 
quantity of sea water weighs 1,026 ounces, its specific gravity being 
called 1-026, that is, taking fresh water as the standard of 
comparison, or 1, 

The densities of the oceans areas follow : North Atlantic, 1 "02664 ; 
South Atlantic, 1*02976 ; the North and South Pacific respectively, 
1-02548 and 1-02658 ; the Indian, 1-0263 ; Mediterranean, 1-0289 ; 
Bed Sea, 1-0286 ; and the Baltic, 1*0086. 

Sea water does not freeze so soon as fresh water (which freezes at 
32°), but remains in its fluid state until the thermometer reaches 



PHYSIOGRAPHY. 85 

281° ^-3 lience it is mucli more serviceable for man. Another point 
worthy of notice is that it is less vapourisable than fresh water, 
causing a less amount of moisture to be carried from its greater 
expanse to the comparitively smaller expanse of land. 

It has been proved by the investigation of the Challenger that 
animals of many orders and genera exist even at the greatest depths 
of the ocean, sponges, molluscs, annelids, crustaceans, &c., having 
been found in great numbers. 

82. Depth, Pressure, and Weight of the Water.— The 

recent soundings of the Challenger prove that our former idea of 
the depth of the ocean was far in excess of the truth, the deepest 
cast being 4,575 fathoms, and the average depth 12,000 feet, or 2^^^- 
miles ; hence its cubic contents equal 145,500,000 x 2i\ = 330,681,818 
cubic miles, or in round numbers 330 millions. The weight from 
the above data may easily be found, but to have it correct we must 
also take into account the pressure at its mean depth, namely, of one 
mile ; the weight of a column of sea water of this height is 1760 x S 
-f 33*8 (height of a column of water equal to the weight of the atmos- 
phere) =156'2 atmospheres; this weight is sufficient to compress 
the water at that depth about '0142,* so that its density will ba 
1*04076. Thus, sea water at its surface has a density of 1"026 (pii^e 
water being 1), but owing to the compression, (1-'0142), or -9854 
cubic feet, at the mean depth, has this density ; hence one cubic foot 
has a mean density of l*026-f-"9854 = l'04076, svipposing the depth 
to be two miles. At this density a cubic foot of sea water weighs 
62-5 (the weight of a cubic foot of pure water) x 1-04076 = 65-0675lb., 
and a cubic mile (5280^ x 65-071b. ) = 4,275,969,078 tons ; hence, entire 
weight of the ocean equals this number multiplied by the number of 
cubic miles, viz., 330 million, which gives 1,411,070 billion tons, or 
about Trrrth of the whole globe. 

83. Its Composition and Saltness.— (For "Composition" see 
45.) The saltness is caused by the presence of soluble matter, as 
sodic chloride (common salt), which exists in a greater quantity than 
any other sahne material ; next to which in abundance come mag- 
nesiaf and lime, which occur as carbonates, sulphates, and chlorides ; 
then follow soda, potash, iron, silica, various iodides &c. Silica and 
carbonate of lime play an important part in nature, supplying the 
skeleton, or hard parts of fishes, shells, and other marine organisms, 
such as form the bottom of the ocean for thousands of square miles. 

Generally the ocean is of a uniform degree of saltness, containing 
about 3 J per cent of saline material. Taking its specific gravity at 2, 

*It has been found by experiment that for every 1,000 feet of depth, water 
Is compressed ^i^th of its bulk. 

t It is the chloride of magnesium which causes the clothes of sailors, when 
wetted with sea water, to have that damp, sticky feeling. 



86 PHTSIOGEAPHT. 

wliich is not far from the mark, a cubic foot would weigh 62-5x2 = 
1251b. ; hence one cubic mile weighs [5380^ x 125) = 8,214,171,428-57 
tons, but the salt is equal to 3^ j)er cent of the whole cubic contents, 
namely, 11,573,863 cubic miles, so that the weight of salt is 
(8214171428x11573868) or 95,069,694,766,186,364 tons, or 95,070 
billion tons nearly. 

The amount of salt in the ocean must ever be on the increase, as 
the rivers in their journeys through the land wash out such soluble 
substances as salt, &c., and carry them into the sea, where 
very nearly all rivers run. When once there it must remain, as in 
the process of evaporation fresh toater alone is taken, which in its 
turn returns with its saline substances. 

Colour. — Though in small quantities the waters of the ocean 
appear colourless, in large masses it is of various hues. For instance, 
in the open sea, it is of a deep blue colour, while in the shallow parts 
it appears green. The cause of these colours has not been satisfac- 
torily explained, some thinking that they are due to the dififerent 
degrees of salt in the water. There are a few sheets of water which 
take their names from their colour, as the Vermilion Sea (Gulf of 
California), the Yelloiu Sea, whose colour is due chiefly to the sedi- 
ment discharged into it by the rivers ; the Green Sea (Sargasso Sea), 
lied, Black, White Seas, &c., whose hues are probalDly due to the 
presence of solid matter, either as living organisms or as sediments. 

The Bottom of the Ocean is somewhat similar to the surface of the 
land — plains at different levels, valleys, and deep depressions, rocky 
ridges, sometimes rising to its surface, forming islands, or sunken 
reefs. It is but the submerged surface of former lands, with the 
exception of coral reefs and submarine volcanoes. 

As a rule, the ocean is shallower near land ; and where the land 
gradually slopes towards the ocean the waters deepen gradually ; 
but where the land descends precipitously the sea deepens in like 
manner, suddenly and abruptly. Thus, on leaving Ireland to cross 
the Atlantic it only sinks 6 feet per mile for the 230 miles ; after- 
wards it makes a descent of 1,400 fathoms in about 20 miles, from 
which there is a plain of nearly 1,200 miles in length. 

84. Movements of the Ocean.— The movements of the 

ocean are of three kinds — namely, ivaves, tides, and currents. These 
motions arise from the influence of the winds, the attraction of 
the sun and moon, and from the temperature. 

Waves are undulations of the water without progressive motion, 
produced by the wind. They vary in size according to the force of 
the wind, from a gentle ripple, to billows 40 feet in height, though 
a wide expanse is requisite to produce its full effect. The highest 
waves known are those which occur off the Cape of Good Hope and 
Cape Horn, where they attain sometimes between 30 and 40 feet 



PHYSIOGRAPHY, 87 

from trough to crest ; but the depth to which the disturbance is felt 
is very slight. The velocity of waves, or the rate at which they 
travel, depends upon the breadth and depth, as a loave of a certain 
ireadth cannot attain more than a certain volocity, and if the depth 
is less than the breadth this velocity cannot be attained. It has been 
calculated that a wave 1,000 feet broad, formed on water 10 feet 
deep, travels 12 miles an hour ; on water 100 feet deep, 36 miles an 
hour, or 53 feet per second ; on water 1,000 feet deep, 49 miles an 
hour. If the wave was 10,000 feet broad, in the depth of 10 feet its 
rate would be 12 miles an hour ; in 100 feet, 39 miles an hour ; in 
1,000 feet, 115 miles an hour; and in 10,000 feet, 154 miles an hour. 
It is not the water which travels at these rates, but simply the 
form of the water, which rises up and down. This motion is well 
imitated by shaking the ends of a stretched rope, giving rise to a 
succession of waves, or also in the shaking of carpets, when the two 
ends held in the hands remain fixed, while loaves are propagated 
from one end to the other. The waves coming near the shore are 
interfered with in their rising and falling by the water causing the 
foot of the wave to be held back, and the head to curve forward, 
and Ireah with great force — the momemtum in some cases being 
that great that large masses of stone or concrete, even weighing as 
much as 50 tons, are torn down from piers and breakwaters. The 
effective pressure of these breakers has been estimated as high as 
6,0001b. per square foot. 

The Tides are occasioned chiefly by the attraction of the moon upon 
the earth, but assisted partly by the sun. Considering the earth as 
a solid, rigid body, the moon's attraction acts upon its centre ; but 
the waters of the ocean directly below the moon experience and 
obey a greater attraction owing to being nearer, thereby causing an 
immense flat wave to be heaped up below the moon. But, at the 
same time, the centre of the earth is attracted more than the waters 
on the other side of the earth, causing a similar wave to be heaped 
up there also ; hence it is evident that it is the difference of th« 
moon's attraction upon the waters on opposite sides of the globe, 
vertically below her, that causes the two tides. 

To make it plainer, let M in the annexed figure represent the 
moon, and E the earth — then the waters at A, being nearer to the 
moon than the centre of the earth 0, are attracted with greater 
force than the earth at (see "Gravitation," 15 and 16), and, being free 
to move, heap them- 
selves in a wave 
directly imder the 
moon, the water 
flowing towards this 
place ; but, at the same 
time, the moon's attrac- 
tion on the centre of '"^'^ Pi^ g 




88 PHYSIOGRAPHY. 

the earth, 0, is much greater than the water at B, owing to the 
same cause ; hence the earth approaches toward the moon, leaving 
the waters behind forming a heap there, so that instead of only one 
tide every 24 hours and 50 minutes we have two, or one every 
12 hours and 25 minutes, both occurring at the same time but on 
opposite sides of the globe, the 12 hours, &c., being taken up by 
the earth in its revolution to the place where the opposite tide took 
place. 

Spring and Neap Tides. — When the sun and moon are on the 
same side of the earth together they evidently act in conjunction. 
This occurs at new and full moon, causing higher or spring tides. 
But when the moon is at right angles (90°) from the sun, when she 
is in her first and last quarters, or half moon, his attraction, being 
exerted at right angles, counteracts the attraction of the moon, 
causing lower or neap tides — the proportion of spring to neap tides 
being as 69 to 31, or nearly as 7 to 3. 

The Tidal Wave. — The earth, by constantly revolving, causes every 
part to be offered in succession to the attracting influence, so that the 
rising waters are drawn along in an immense tidal wave around the 
globe ; and had the surface of the earth been entirely covered with 
water the tidal wave would have been regular and continuous in its 
journey from east to west ; but such is not the case, owing to the 
many interruptions of the land causing it to be deflected into 
various courses. The tidal wave may be regarded as receiving its 
first impulse in the Southern Ocean, where the greatest uninterrupted 
expanse of water occurs. From here it is carried northward into the 
Indian, Atlantic, and Pacific Oceans, where it unites with the minor 
tide waves generated in these oceans. It there subdivides, flows, 
rises, &c., according to the depth of water and the obstructions of 
coasts and islands. Its velonty varies much. For instance, it 
crosses the Indian Ocean in six hours, entering the Atlantic, 
travelling through it at the rate of from 500 to 700 miles an hour 
till it reaches the West of Ireland, reaching the Orkneys and Bergen 
at the same time, and travelling now as one branch through the 
North Sea it reaches Aberdeen in thirty-seven hours, and London 
twelve hours later, or in forty-nine hours from the time it left its 
antipodes. 

By noting the times at which the same high water reaches 
different parts of the coast a series of lines connecting these points 
may be laid down so as to indicate the course of the tidal wave with 
great precision. These series of lines are termed co-tidal lines. The 
height of the tidal wave in the Pacific seldom exceeds two or at the 
most three feet ; in the Indian and Atlantic Oceans it reaches eight 
or nine feet ; but in bays and gulfs, opening broadly to its course 
and narrowing toward the interior, as the Bristol Channel, the Bay 



PHYSIOGRAPHY 89 

of Biscay, Bay of Fundy, &c., it may rise from thirty to seventy feet. 
When the seas terminate in river estuaries, the tide, being converged, 
rushes up the river with great force and speed. It is then called 
a bore, examples of which occur in the Severn, where a bore rises 
nine feet high ; in the Amazon, thirteen feet ; Hooghly, twenty to 
twenty-five feet ; Tsien-tang, thirty feet. But, on the other hand, 
in inland seas and gulfs, the openings of which are narrow, and lie 
transversely to the course of the tidal wave, little or no tides are 
experienced, as they are not of sufl&cient area to form any perceptible 
one of their own, examples of which are the Mediterranean, Baltic, 
&c. 

85. Currents, their Causes, &C. — Currents are movements in 
the ocean, like great rivers, transporting the waters from one region 
to another. These currents, like the winds, are arranged as constant, 
periodical, and variable. The constant depend chiefly upon the 
unequal temperatures and densities in the waters of the ocean, the 
rotation of the earth, and the trade winds. The heat of the sun at 
the tropics heats and expands the water there to a considerable 
depth ; at the same time the cold at the poles renders the water 
heavy and dense, causing it to sink and flow below the warm water 
lying near the equator, while the lighter water of these regions flows 
over towards the poles to restore equilibrium. These currents do not 
flow exactly north and south, but are deflected in like manner to the 
trade winds, the polar currents tending to the west and the equatorial 
to the east (see 104), forming, the same as in the air, four great 
currents. The periodical currents are caused by the tides, monsoons, 
sea and land breezes within the tropics, &c. They are most common 
in the Indian Ocean. The variable currents are those produced by 
local peculiarities in the tides, winds, melting of ice in the polar 
regions, and other such causes. Drift currents, due to the long- 
continued agency of the wind, afi*ect only a very trifling depth. Deep 
sea currents, as their name indicates, penetrate to great depths, 
namely, hundreds of fathoms below the surface. 

The currents of each ocean will be described in their proper place, 
under each ocean. (For situation and extent of the ocean, see 67.) 

The Atlantic Ocean. — ^We will notice this one first, not on account 
of its size but of its great importance to us. This ocean is calculated 
to drain more than 19,000,000 square miles of land. It is also 
distinguished from its fewness of islands but numerous gulfs and 
arms. Its average depth, as ascertained by the Challenger, is about 
2,500 fathoms, or 15,000 feet, its greatest known depth being 3,916 
fathoms, or 23,500 feet. In the northern part, near the middle, ifc 
is a flat plain, running north and south, the average depth of this 
plain being about 1,800 fathoms, though at each side, and south of 
the equator, it is, on an average, about 2,800 fathoms. Round the 



90 



PHYSIOGRAPHY. 



Britisli Isles the portions of this ocean are not very deep, no part of 
the German Ocean exceeding 70 fathoms ; and the deepest between 




I 



Fig. 9.— Section of Equatorial Atlantic. 



tSfRMlrffA 




Fig. 10.— Section of the North, Atlantic. 

Dover and Calais does not exceed 30 fathoms. The temperature of 
the upper layer, of about 100 fathoms deep, may be said to average 
between 75° and 80° in summer, ranging down to about 55° in 
winter. Below this depth th effect of the sun is not felt, sinking 
from 55° at 100 fathoms to about 35° at 2,000 fathoms. The S.W. 
Atlantic is still colder, the bottom water averaging from 31° to 33^°. 
The principal branches and inlets belonging to this ocean are the 
North Sea, Baltic Sea, Irish Sea, the English Channel, the Bay of 
Biscay, the Mediterranean, &c., on the east side ; Hudson Bay, Gulfs 
of Mexico and St. Lawrence, the Caribbean Sea, &c., on the west. 
(For its chief affluents see "Table of Rivers," page 99.) Among 
its currents the principal and better known are the Equatm^al, the 



i 



PHTSIOGEAPHT. 91 

Gulf Stream, the Arctic, tlie Guinea, qmS. th.Q Brazil. The first, aa 
its name implies, occurs chiefly in the region of the equator, flowing 
along the western coast of Africa, and crossing the ocean towards the 
American continent. After traversing a little more than half way 
it divides into two branches, one going northward by the coast of 
Guiana into the Caribbean Sea, the other, the weaker part, travelling 
southward along the shores of Brazil. This equatorial current, from 
the coasts of Africa to the Caribbean Sea, is nearly 4,000 miles in 
length, and varies in breadth from 150 to 450 miles. Its velocity 
ranges from 18 to 30 miles a day at the surface, its rate decreasing 
lower down till at the bottom it never exceeds 12 miles. The Gulf 
Stream is by far the most important current of this ocean. It leavea 
the Gulf of Mexico, and travels through the Strait of Florida at a 
meati velocity of 46 miles a day, its average temperature being a 
little over 8C°. Flowing northward, almost parallel with th3 
American coast, at latitude 40° north it turns to the east, touching 
the south banks of Newfoundland, and proceeds .across the Atlantic 
to the Azores, where it divides into two large branches, one going 
north-east and onward till it reaches the Arctic Ocean, and the other 
Bouth-east to the west coast of Africa. The entire length of this 
vast river, from the Gulf of Mexico to the Azores, is 3,000 mUes, 
and its greatest width about 112 miles. Its velocity gradually 
diminishes from 46 miles a day at starting to 18 at the Newfound- 
land banks, stUl getting weaker as it crosses the Atlantic and also 
decreasing in temperature, gradually diflusing its heat all around. 

The water of this stream is Salter than that of the common sea 
water, of a more bluish colour, and possesses very little affinity for 
the ordinary water ; even so that in many places you may see with 
the naked eye where, on either sides, it touches the neighboiu-ing 
water. It is owing to this stream that many places may enjoy a 
summer climate all the year round, as on the coast of France. 
England enjoys a temperate climate owing to the same cause ; 
while other places in a lower latitude experience much more severe 
winters, &c. (See "Climate" 116.) 

The Arctic current of cold water flows along the east coast of 
Greenland ; being met by another south of Cape Farewell from Davis 
Strait they flow on southward towards the Caribbean Sea. It 
divides on meeting the GuK Stream, part flowing to the Caribbean 
Sea, entering as an under current, the othfc^ ^jart, journeying south- 
west, forming the United States counter current. It is this current of 
cold water which replaces the warm water sent through the Gulf 
Stream, and also modifies the climate of all the United States coast- 
line, &c. 

The Pacific Oceak. — It is in this ocean that the greatest depth 
has been found in the late expedition, viz., north of Papua, in lat. 
11° 23' N., long. 143° 16' E., the depth being 4,575 fathoms, or 



93 PHYSIOGRAPHY. 

27,450 feet, about 5-|- miles. The average depth of the South Pacific 
is about 2,000 fathoms, and that of the North Pacific about 3,000 
fathoms, increasing gradually from south to north. The surface 
temperature of this ocean may be taken in summer at about 80° F, ; 
at a depth of 80 fathoms near Tahiti it is 77° R, but 500 fathoms 
deep the temperature is uniformly about 44° P. ; at a greater depth 
than this it falls gradually to 36°, and sometimes even to 32°. 

The chief branches and arms are : Behring Sea, the Gulf of Cali- 
fornia, and Bay of Panama on the east, and Sea of Japan, Yellow 
Sea, China Sea, &c,, on the western side. This ocean contains a vast 
number of islands, both of volcanic and coral formation. A glance 
at a map will be of more service than a written description of their 
situation. The chief current is the equatorial, which originates in 
the Antarctic drift current, flowing north-east till near the coast of 
Chili, where it divides, sending one branch round by Cape Horn, and 
forming the current of that name. The other part travels north- 
ward, forming the Peruvian current, which is so remarkable on 
account of its cold stream along the hot coast of Africa. On the 
Peruvian coast, in lat. 18° S., it has a temperature of 14° below that 
of the neighbouring ocean, and even at lat. 8° S., where it branches 
off to the west, joining the great equatorial current of the Pacific, 
its temperature is between 9° and 10° colder than the other water. 
The chief current now continues until it forms, northward of the 
Philippine Islands, the Japan current, or what we may term the 
Gulf Stream of the Pacific — it now performing similar duties to the 
one of the Atlantic. Travelling nearly to the Aleutian Isles, it sweeps 
round and returns to the equatorial current. The southern part of 
the equatorial current journeys along southwards to the coast of 
Australia under the name of New South Wales current, and then 
wends its way to the Antarctic Ocean. 

The Indian Ocean. — The greatest depth hitherto known in this 
ocean was 2,340 fathoms, or 14,040 feet, lying to the east of Ceylon, 
long, 85° ; but from recent occasional soundings the depth of more 
than 20,000 feet has been ascertained in the south-west portion of 
ithis sea. The principal branches and arms of this ocean are, the 
Arabian Sea, Persian Gulf, Gulf of Oman, Gulf of Aden, Eed Sea, 
Mosambique Channel, &c., on the west ; the Bay of Bengal, and the 
Great Australian Bight, &c., on the east. The equatorial current in 
this ocean travels westward from the Indian Archipelago and Aus- 
tralia to the east coast of Africa, where, divided by the island of 
Madagascar, one branch flowing round the north of the island, 
forming the Mozambique current, the other southward towards 
the Cape of Good Hope, they again unite, forming the Cape current, 
part of which flows northward into the Atlantic, while the chief 
part is deflected to the east by the Agulhas Bank, and flows to 
AustraKa. This current is of much importance to vessels on their 



PHYSIOGRAPHY. 93 

journey to Australia, travelling as it does at the rate of about 4| 
miles per hour. 

The Arctic Ocean. — This ocean does not appear near so deej^ 
generally as those previously mentioned, especially in the higher 
latitudes. The temperature reaches in the lower parts, as low as 72"^ 
helow zero, but in the summer about 32° at the surface. The chief 
branches are the White Sea, the Gulfs of Kara, Obi, Yenisei and 
Behring Strait, in the Old World ; and Melville Sound, Barrow Strait, 
Baffin Bay, &c., in the New World. The comparatively warm Gulf 
Stream flowing into this ocean causes the colder water to flow off 
as the Arctic current. (See " Atlantic Ocean," 89.) 

The Antarctic Ocean. — This ocean has not been traversed as far 
as lat. 80° on account of its being much colder than in the Arctic 
Ocean ; but the part that is known is much deeper than the water 
at its antipodes, the greatest depth being 1,975 fathoms, or 11,850 
feet. The temperature of the water is lower here than in any other 
ocean. The surface water in February, in latitude 5J° S., and longi- 
tude 79° 50' E., was about 28J° F. in the pack ice ; but a short distance 
from it the temperature was found to be 32° F., gradually sinking as 
the depth increased, till, at 40 fathoms deep, it was 29°, this tempera- 
ture remaining constant for 260 fathoms deeper, when it began to 
rise, reaching 32° or 33°. In this ocean several valuable ocean cur- 
rents have their origin. One of the chief is the Antarctic drift 
(which is described under the name of Equatorial current), in the 
Pacific. 

88. Action of the Sea on the Earth's Crust.— The sea coasts 

are subject to the erosive and destroying movements of the ocean, 
especially breakers, which are aided in their action by the tides. 
These breakers, which are simply the wind waves (which see) formed 
on the surface of the sea during storms, acquire immense force, and 
break with violence on the rocky shores. One thing that assists 
marine denudation much, is the fact of large stones or any matter 
having from one-third to one-half of their weight balanced by the 
buoyancy of the water. Hence the breakers have only about half 
the work to do to remove the stones, &c., when in the water. The 
work of the sea on the coast is not that of carving or cutting out, but 
simply that of levelling. The rate at which the sea wastes the land 
depends on its nature, and also on the alterations of the rocks of the 
coast, aa well as on the force and direction of the currents. Thus 
on the east coast of this country, where the rocks are principally 
sands, clays, &c., the destruction is very great. On the coast of 
Yorkshire the waste is from one to four yards per annum. 

Again on the south coast we see several cHffs, headlands, &c., still 
standing contending against the action of the sea, while the soft 
sandstones have given way much more rapidly. Yet still, though 



94 PHYSIOGrvAPHY. 

these cliifs, &c., are composed of much harder rocts, they cannot 
hold their ground, but slowly, yet surely, are compelled to retreat 
before the action of the waves, which scoo^J them out near the 
ordinary sea level, causing the weight of the overhanging portion to 
outbalance the cohesion of the rocks. The force of breakers in 1829 
(November) washed about like pebbles blocks of limestone and 
granite, from 3 to 5 tons in weight each, near the breakwater at 
Plymouth, carrying 300 tons of them a distance of 200 feet. 
Another, 7 tons in weight, was washed 150 feet up the incUned 
plane of the breakwater. Striking examples of the sea's action may be 
noticed in the many rocks which stand out in the sea detached from 
the main mass of land, but which have evidently formed part of it, 
such as the Needles, off the Isle of Wight, and the Drongs of Shet- 
land. To the sea's action may be attributed the piling up of shingle 
beaches. The shingle is projected on the land beyond the reach of 
the retiring waves, forming in many places beaches several feet in 
height. 

Inland Seas. — The Mediterranean Sea, between Europe and Africa, 
has an area of about 950,000 square miles ; mean depth 1,200 
fathoms, varying from 300 to 500 at the Strait of Gibraltar to 2,000 
fathoms in the east. The average temperature is 60° to 70°. The 
Black Sea, including the Sea of Azov, has an area of 185,000 square 
miles ; depth about 50 fathoms. The Caspian Sea may be regarded 
as the greatest salt water lake in the world. It is situated 81 feet 
below the sea level ; its area is about 177,000 square miles, and the 
depth varies from 8 fathoms in the north to 450 in the south ; the 
mean temperature is about 56°. The Red Sea has an area of 175,000 
square miles ; the average depth is 200 fathoms ; temperature, 96° 
to 106° F. The Baltic Sea has an area of about 162,000 square 
miles ; average depth about 800 feet ; average surface temperature 
35° in the north and 45° in the south. 

WATERS OF THE LAND. 

87. Springs, Rivers, Lakes, Sec— Springs are principally 
of three kinds — land, artesian, and mineral. The former occur 
in places where the bed of rock is pervious to water, being 
underlaid by a bed that is impervious, the rain sinking through 
the top layer, forming pools on the underlying impervious 
substratum, and when a well or a pond is dry the water collects 
in it. These depend almost entirely on the rainfall, and are 
also hable to be tainted with matter from the sewers, &c. The 
deep-seated are just the reverse of these, being but little influenced 
by summer droughts or winter rains, flowing steadily at aU times. 
Perennial spi'ings are those which flow year after year without any 
signs of abatement. 



PHYSIOGRAPHY. 



95 



Artesian, or Transtratic, Springs result from one permeable stratum 
lying between two impermeable strata, the water piercing into the 
rock where the layer is at or near the surface. It then ruTis through 
it in the direction of the slope of the layer until it has reached the 
surface in some other place. It will perhaps be better understood 
from the following diagram, where H B represents the permeable bed. 




Kg. 11. 
C and D the two impermeable beds which it lies between after 
leaving H ; then, the water soaking into the earth at H, wiU soak 
down as low as possible, namely to the bed D, and afterwards 
gradually flow through the pervious bed H B, imtil it reaches B, 
when it rushes out as a spring. It is this class of springs which gives 
rise to artesian wells, as, for instance, suppose, as at 0, the top layer 
be pierced down to the water-bearing strata, it is evident the water 
will rise at 0. 

Mineral or Deep-seated Springs usually contain gases, salts, minerals, 
acids, bitumen, organic matter, &c., examples of which occur at 
Cheltenham, Epsom, &c., where they are saline, containing salts. In 
Italy and France they are calcareous, containing much lime. In the 
latter country there are more than 900. They are termed chalybeate 
when iron is present, as at Tunbridge Wells, sulphurous when 
containing sulphur, and carbonated when containing carbonic acid. 

Germany and Spain have large numbers of these springs — about 
600 in the former country and 400 in the latter. (See " Geysers 
and Hot Springs," 54.) 

88. Rivers are of great importance in nature by carrying off the 
surplus water into the ocean, and also by giving rise to the most 
fertile parts of the coimtry They are also of importance in a com- 
mercial respect, and the benefits arising therefrom may be noticed in 
such places as London, Liverpool, &c. The basin of a river is the' 
whole tract drained by the river and its tributaries, the area of which 
may be found by drawing a line connecting the source of the river 
with the sources of all its tributaries. The elevated ridge which 
separates one river basin from another is termed the 2oatershed, or 



96 PHTSIOGRAPHT. 

water parting J as it is now called, tlie former word being now used 
to denote the sides of the hills sloping from the ridge towards a 
river. To have a good knowledge of all the chief slopes, &c., the 
student should consult a good map of the Physical Features of the 
World — or better, one of each country. The area of the basin of 
each river may be traced on the map, as before mentioned. Eivers 
have their sources in springs, snow melting on the tops of mountains, 
glaciers, lakes at the base of mountains, &c. 

The importance of a river depends chiefly on the permanence of 
its volume, depth, velocity, nature of channel, accessible entrance, &c. 

The volume depends chiefly on the extent of country drained by 
its affluents, which in temperate zones is generally lessened in 
summer and increased in winter ; but, on the whole, the supply is 
pretty equable. In tropical countries, where the rain falls and snow 
melts at regular seasons, the rivers flow the country periodically. 
The velocity depends mainly on the slope and the nature of its 
channel, according to whether it is straight, deep, &c., or the reverse, 
and also upon the height of its source. The average slope is about 
2 feet in a mile, or 1 in 2640. When it exceeds 1 in 250 it is 
unnavigable. A greater slope forms rapids, and a perpendicular 
descent a cascade or cataract. 

The most remarkable waterfalls are : — 

Total Height. 

Oreo Falls, at Monte Kosa (Alps) 2,400 feet. 

Gavarnie, in the Pyrenees 1,400 „ 

Staubach, Switzerland 1,000 „ 

Maaneloan, Norway 940 „ 

Victoria Falls, on the Zambesi, Africa 100 „ 

Murchison Falls, on the Nile, Africa ^ 120 „ 

Niagara Falls, on the River Niagara 160 „ 

Missouri (Great Falls) 75 „ 

Eiakan-f OS, near Christiania 900 „ 

The erosive and transporting powers of a river depend nearly entirely 
on the rapidity of the currents — those, for instance, which run down 
the mountain sides, having a great slope and a swift current, will cut 
out deep gorges and ravines at the bottom. It has been calculated that 
a velocity of 3 inches per second will lift up fine clay ; that 6 inches 
will hft fine sand ; 8 inches, course sand ; and 12 inches, gravel ; 
while a velocity of 24 inches per second will roll along rounded 
pebbles an inch in diameter ; and at three feet per second, angular 
stones of the size of an egg. A fine example of the erosive powers 
of rivers is exemplified in the river Niagara, where it is proved that 
the waters at the falls have cut back their passage about seven miles, 
forming a gorge 200 to 300 feet in height, and 600 to 1,200 feet in 
width, the average rate of recession being about 1 foot per annum. 



PHYSIOGKAPHY. 97 

The amount of matter transported to the sea and other places by 
rivers is simply astounding. The slow rivers deposit a considerable 
portion in their course, as the Amazon, Ganges, &c., but the short 
and rapid ones carry it forward. The river Rhine, for example, 
carries past Bohn about 400 tons in one hour, or between 3 and 4 
million tons in a year ; and the Ganges, during the 122 days of niiny 
season, caiTies 339,413,760 tons past Ghazepoor, 500 miles from the 
sea — large islands having been made in its channel even during a 
man's lifetime. 

The principal rock-constituents carried in suspension by rivers are 
quartz, or some very siliceous mineral, and, in solution, common salt 
(sodic chloride), sulphates of lime and magnesia, carbonate of soda, 
and carbonate of lime. The substances held in solution still remain 
so, causing the saltness of the ocean (see 83), while those in suspen- 
sion are deposited. 

89. Deltas. — The detritus transported by the rivers at their 
mouths has a tendency, especially in tideless or nearly tideless seas, 
to form more or less extensive flat plains at the point where the 
waters have lost their transporting powers, mostly commencing at 
the centre of the river's mouth, forming- an island, which gradually 
widens and extends till a triangular space is formed by the deposit, 
the apex being directed up the river. The deltas of the Nile, Danube, 
Volga, Rhone, and Po are examples of those formed at the mouth of 
tideless rivers ; but one of the most remarkable is the delta of the 
Ganges, the base of the triangle being 200 miles, and its side 220 
miles. The delta of the Mississippi covers an area of 15,000 square 
miles, but is divided into innumerable lakes, marshes, &c. It has 
been calculated that this river carries down to its mouth 
28,188,803,892 cubic feet of sediment per annum, or one cubic mile 
in less than 5| years. 

90. Eiver Systems.— The rivers of the world are all classed 
into four great systems. (1) Arctic; (2) Atlantic; (3) Pacific; 
(4) Indian. Thus, the Danube, Dneiper. &c., may be said to com- 
pose the Black Sea System ; but the Black Sea is only an arm of the 
Mediterranean, which in its turn is only an inlet of the Atlantic; 
hence the Danube, Dneiper, &c., belong to the Atlantic. There are 
a few, however, not in communication with the ocean, losing them- 
selves in sandy deserts, &c. These are termed Continental Systems, 
the most noted of which is that which empties itself in the Aral or 
Caspian Sea. It is estimated that the Atlantic drains 19,050,000 
square miles ; the Arctic, 7,500,000 ; the Pacific, 8,660,000 ; the 
Indian, 6,300,000 ; and Contmental, 10,673,000. 

G 



98 



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PHYSIOGRAPHY. 103 

91. Lakes are large collections of water formed in the depressions 
of the earth's surface. They are generally classed into four or five 
kinds, but belonging to two natural divisions, viz., (1) Those which 
once formed part of the sea but have been cut off by the elevation 
of a portion of the sea bed, as the Caspian and Ai*al Seas ; and 
(2) Depressions in the surface of the land, which receive a portion of 
the drainage, as the great lakes of Ainerica, and most others, 
(a) Lakes that both receive and discharge rivers, which are in most 
cases only expansions of the stream. Their water is always fresh, 
examples of which are the great American and African lakes. These 
lakes are sometimes called lakes of transmission. (6) Lakes which 
receive no streams but discharge water by their own, the supply 
being kept up by springs. They are mostly small and fresh. 
The sotxrce of the Volga is a lake of this description in the Valdai 
Hills. They are termed lakes of emission, (c) Those that receive 
water but have no visible outlet, the waste by evaporation being 
supposed to be equal to the supply. The lakes of this description 
are generally large, and either salt or brackish, such as the Caspian, 
Aral, and Dead Seas, Lakes Balkash, Van, &c. {d) Those which 
neither receive rivers nor have any visible outlets. They are 
generally of small size, and occupy craters of extinct volcanoes, as 
Lake Albano, near Rome. 

Distribution and Areas of Lakes. — Lakes have a peculiar tendency 
to occur in groups. For instance, in North America there is the 
series consisting of Lakes Superior, 32,000 square miles ; Huron, 
24,000 ; Michigan, 20,000 ; Erie, 9,600 ; Ontario, 6,300 ; the Great 
Bear, 19,000 ; Great Slave, 12,000 ; Winnipeg, 9,000 ; Winnipegosis, 
3,000'; Athabasca, 3,000 ; Manitoba, 2,100 ; Deer, 2,400 ; Wollaston, 
1,900. In Asia they occur as three distinct groups. Many of the 
lakes in this country are salt or brackish, the cluef of which are 
the Caspian (inland sea) ; Aral, 26,000 square miles ; Balkash, 7,000 ; 
Urumiah, 1,800 (26-24 percent saline matter) ; Van, 1,600 ; Tongri- 
nor, 1,800 ; Koko-nor, 1,500 ; Lob, 1,300 ; Dead Sea, &c. Of the 
fresh water lakes the principal are Baikal (Holy Sea of the Russians) 
in Siberian Tartary, 14,800 square miles ; Tong-Ting, 2,000 ; Booka- 
nor, in Thibet, 1,000 ; Zaizan, 1,000, &c. In Africa the principal 
axe the Victoria and Albert Nyanza, Tanganyika, Dembea (1,400). 
In Europe the principal lakes occur as a group in Finland and 
Russia. They are Ladoga, 6,633 square miles ; Onega, 3,280 ; 
Saima, 2,000 ; Peipns, 1,250 ; Enara, 1,200— which all occur in a 
circumscribed area. Others occur in Sweden, namely, Wener, 2,130 
square miles ; Wetter, 840 ; Maelar, 760, &c. Small lakes occur 
abundantly in the mountain regions, and are remarkable for their 
lovely scenery, examples of which are our own — namely, those in 
Scotland, the north of England, the south of Ireland— and the 
much greater ones of the Alps, The chief of the Alpine lakes are 



104 PHYSIOGRAPHY. 

Geneva, 240 square miles ; Constance, 228 ; Garda, 182 : Maggiore 
150. 

Neufchatel, 114 square miles ; Lucerne, 98 square miles ; Zuricli, 
74 square miles, &c. Those in the British Isles are Loughs Neagh, 
150 square miles ; Corrib, 63 square miles ; Erne, 56 square miles, 
&c., in Ireland. Loch Lomond, 40 square miles, &c., in Scotland. 
Windermere, 10 square miles, &c., in the Cumbrian Hills. 

The most elevated lake is Sir-i-kol, 15,600 feet, in Central Asia ; 
Tuz-Gul, in Asia Minor, the saltest known, containing 32 per cent 
of saline matter ; Urumiah, 26 '24 per cent ; the Dead Sea, 24 per 
cent ; and Lake Elton, situated in the Steppe, 70 miles E. of the 
Volga. 

The uses of lakes are, (1) Acting as regulators to rivers, and pre- 
venting the too rapid flow of the waters during excessive raiufaUs ; 
(2) Acting as settling ponds for the water to purify in ; (3) Serving to 
temper the climate, especially when occuriug in the central part of 
the continent. 

THE ATMOSPHERE. 
92. Compositon of the Atmosphere. — The envelope of 

gaseous matter which surrounds our earth is called the atmosphere''' 
or atmospheric air. It is a mixture (not a chemical compound, each 
gas still possessing its own peculiar property) of oxygen and nitrogen, 
contaminated with a very small, but variable, proportion of carbonic 
acid and water in the state of vapour. It consists by weight of one 
atom of oxygen to two of nitrogen, and by volume of one part 
oxygen to four nitrogen, nearly ; or, more exactly, its percentage is 
79'5 nitrogen (N), 20 oxygen (0), "45 aqueous vapour (HgO), and '05 
carbonic acid (COo). Though nitrogen forms by far the greater 
pa,rt of the air, oxygen is the most important, as without it no 
animal could live or fire burn, for it is this gas that purifies the 
blood, keeps \ip its natural warmth, and is the supporter of flame. 
Nitrogen may be termed the agent by which oxygen is held in check 
by diluting it. The air in its diluted state forms the food upon 
which the vitality of both animals and plants is sustained ; but, 
while it is inhaled by both in breathing, animals exhale carbonic 
sicid, and carbonic acid is inhaled and assimilated by plants, which 
in their turn exhale oxygen, thereby keeping up the equilibrium or 
balance. 

Though, as above stated, the air is not a chemical compound, but 
simply a mixture, yet it has much permanence of character, its two 
chief elements being found nearly in the same proportion in all 
cHmates and altitudes. 

* AtTMS, vapour. Sjphaira, a sphere. 



PHYSIOGRAPHY. 1C5 

93. Pressure of the Atmosphere.— Air, like other perfect 

gas, exerts an expansive force directly proportional to its density. 
This force is measured by means of the barometer, the pressure per 
square inch being equal in weight to a column of mercury supported 
in a barometric tube, the area of a section of which is one square 
inch, the mean height of which at the level of the sea is 30 inches, 
and its weight about 14|lb. (147304) avoirdupois, which is, there- 
fore, the mean pressure of the atmosphere per square inch. The 
pressure and density of the air are regulated by the following law : 
At the same temperature the elastic forces, or pressure, of two portions 
of air are in direct proportion to the densities, or in inverse propor- 
tion to the spaces occupied by these portions. The atmosphere is 
much denser near the level of the sea than at some distance above 
it, owing to its being confined to the surface of the earth by 
gravitation ; or, in other words, being pressed down by the weight 
of that which is above. The density rapidly decreases the higher 
we ascend. For instance, at an elevation of three miles it is one-half 
the density it is at the earth's surface ; at six miles it is one-fourth, 
at nine miles one-eighth, at twelve miles one-sixteenth, and so on, 
the density decreasing in geometrical 'progression as the height increases 
in arithmetical progression. 

The pressure of the atmosphere is exerted on all substances, both 
internally and externally. The body of a man of ordinary stature 
has an area of about 2,000 cubic inches, hence the pressure on the 
body will be 147304 x 2,000 = 29,460-81b. But how is it, it may be 
asked, that this immense weight does not crush the man ? The 
answer is that the air within the body and its pores counterbalances 
the weight of the external air. On every square mile the pressure, 
or weight, is 26,345,088 tons ; so that the total pressure on the 
earth's surface is 5,189,982,336 million tons. 

94. Height of the Atmosphere.— From the law given above, 
regarding the density of the air the higher we ascend, it is evident 
that the greater part of the atmosphere is always within 32 miles of 
the surface of the earth, but how far it really extends is extremely 
tincertain, though it may with safety be afiirmed to reach the height 
of 45 miles, where it is about 25,000 times rarer than at the level of 
the sea. Even at the height of &ix miles the air is so rare that man 
can hardly breathe. Though the greater part of the atmosphere is 
always within 30 miles or so from the surface of the earth, yet it is 
very probable that even at the height of 250 miles a very rare 
atmosphere exists. 

Not only does the pressure decrease the higher we ascend, but 
also the temperature, though not at such a constant ra+e. The 
atmosphere being the medium throvigh which the sun's heat is con- 
veyed to and from the earth, the lower and denser strata or layers 



106 PHYSIOGRAPHY. 

absorb the greatest amount, and are necessarily the warmer. In 
ascending mountains the decrease of temperature averages about 
1° F. for every 300 feet. The averages, according to Mr. Glaisher, 
in his balloon ascents made in this country, when the sky was partially 
clear, are as under : — 

Number of feet 

Elation to feet. TSSSn'" 

of r F. 

to 1,000 140 

1,000 „ 2,000 190 

2,000 „ 3,000 220 

3,000 „ 4,000 290 

4,000 „ 5.000 370 

5,000 „ 10,000 370 

10,000 „ 20,000 470 

20,000 „ 30,000 820 

95. Weight of Air. — That air has weight may be easily proved 
in the following manner : Take a vessel measuring 10 inches in 
length, breadth, and height, and provided with a stop-cock. Let its 
weight be accurately determined. Exhaust the air from it by means 
of an air pump, turning the stop-cock immediately ; then, on 
weighing again, it will be found to have lost 310 grains, which is 
evidently the weight of the air contained in the vessel — namely, 
10^ = 1,000 cubic inches ; or 1 cubic foot of dry air, at 60° F., weighs 
about 535 grains. 

96. The Barometer is an instrument to measure the weight or 
pressure of the atmosphere, and thereby to indicate the variations of 
the weather. It consists of a cylinder or tube, from which the air 
has been exhausted, closed at one end, the open end being inserted 
in a cup of mercury, on which the ]pressure of the atmosphere is 
exerted, forcing the mercury up the tube (there being no pressure 
there) until it reaches the height of 29*94 inches, when the weight 
of the column of mercury equals the pressure or weight of the 
atmosphere on the surface outside the tube. Supposing water to 
be used instead of mercury, the column would be about 33-8 feet, 
or 13'568 times the height of the mercury, through the latter being 
that many times heavier than water. As the air varies in weight or 
pressure it is evident that it will influence the mercury in the tube, 
which will rise and fall in exact proportion with the pressure. The 
column of mercury in the barometer undergoes several regular 
variations in the course of the day, which are termed liorary 
'variations. According to Humboldt, the maximum elevation at the 
equator takes place about nine o'clock in the morning, after which 
hour it becomes less until about four or half-past in the afternoon, 
attaining its minimum. It again ascends until eleven at night, 



PHYSIOGRAPHY. 107 

when it attains its second maximum, once more descends till four, 
reaching its second minimum, and then starts on its journey back 
until nine. It has also been noticed that the elevation of the 
mercury at noon corresponds almost exactly with the mean diurnal 
height. These variations are due to the action of the sun's rays 
upon the air and vapour atmosphere. The mean pressure of the 
atmosphere is also subject to an annual oscillation, the amount of 
which, except for some particular places, has not yet been ascertained. 

GENERAL RULES PROGNOSTICATING CHANGES IN THE 
WEATHER BY MEANS OP THE BAROMETER. 

97. The following rules, which are without doubt the best 
yet given by any authority, are those of Patrick. (1) The rising of 
the mercury presages, in general, fair weather, and its falling the 
contrary, as rain, snow, high winds, and storms. (2) In very hot 
weather the falling of the mercury indicates thunder. (3) In winter 
the rising presages frost ; and in frosty weather, if the mercury 
falls three or four divisions (tenth of an inch), there will certainly 
follow a thaw ; but in a continual frost, if the mercury rises there 
wiU be snow. (4) When foul weather happens soon after the falling 
of the mercury, expect but little of it ; and, on the other hand, little 
fair weather may be expected when it becomes quickly fair after the 
rising of the mercury. (5) In foul weather, when the mercury rises 
much and high, and so continues for two or three days before the 
foul weather has gone away, then a continuance of fair weather may 
be expected to follow. (6) In fair weather, when the mercury falls 
much and low, and thus continues for two or three days before the 
rain comes, then a great deal of wet may be expected to follow. 
(7) The unsettled motion, or frequent rising and falling, of the 
mercury denotes changeable weather. (8) The chords on the scale 
are not so strictly to be observed as the rising and falling of the 
mercxu-y, for if it stands at much rain and then rises to changeable 
it presages fair weather, though not to continue so long as though 
the mercury had risen higher ; and so, on the contrary, if the 
mercury stands at fair and then falls to changeable it presages foul 
weather, though not so much as if it had sunk lower. 

98. The Barometer is also useful for measuring the heights of 
mountains or the height of the country above the sea level, &c., 
though for this purpose very accurate instruments are required, 
such as Roughton's portable ones. As we ascend from the level 
siu-face of the earth the column of atmosphere pressing on the 
mercury becomes lighter by the removal of the subjacent stratum, 
hence the fluid falls in the tube of the barometer. For ordinary 
purposes the following very simple rule by .Sir John Leslie is 



108 PHTSIOGRAPHY. 

sufficiently accurate : Mark the height of the mercury in the 
barometer at the bottom of the height to be measured, and also at 
the top ; then, as the sum of the heights of the mercury at the 
bottom and top stations is to their difference so is 52,000 to the 
height to be measured in feet. Another rough rule is — Multiply 
the difference of the logarithms of the barometric heights by 1,000, 
and the difference of the levels will be obtained in fathoms. 
Generally for every inch that the mercury falls we may reckon 992 
feet. The reverse to finding the heights of mountains, &c. — namely, 
estimating the depth of pits — may be found with equal facility by 
the aid of the barometer. For instance, at a depth of 15,000 feet it 
stood at 32 '28 inches, while one at the surface stood at 30'518. 

99. The Atmosphere in Relation with Light.— The 

atmosphere is the medium by which the sun's heat and light are 
conveyed to this earth. Each ray proceeding from the sun consists 
of two distinct parts — the one producing light, the other heat. 
Heat and light are alike indispensable to plants and animals, and 
are so reflected (turned back) and diffused by the atmosphere as to 
become most available to vegetable and animal life. White light is 
a combination of red, orange, yellow, green, blue, indigo, and violet 
rays. Vapour, whether in the atmosphere or sea,, absorhs all the 
coloured rays except blue ; hence the colour of the ocean and sky, 
the sky always appearing of a much darker colour than the tops of 
high mountains. Not only is light absorbed by the atmosphere, but 
reflected, refracted, and diffused or dispersed. As soon as the rays meet 
the earth's atmosphere a portion is reflected, the remaining portion 
being refracted or bent on entering the air. Some of the portions, 
in their journey to the earth, are absorbed, while others are dispersed^ 
thereby causing each ray to illuminate a much greater space than if 
there had been no atmosphere to have disturbed its course, so 
that valleys and surfaces not directly exposed to the sun are lighted. 
If the rays fall vertically, only eight out of every ten reach the 
earth's surface. The greater the angle of inclination the greater the 
number absorbed. When the sun is rising or setting we can gaze 
on it with ease, owing to this ; as, for instance, when it is horizontal, 
only five rays out of every 10,000 reach the eye of the observer. It 
is to the refraction of the sun that we owe that dim light called 
twilight, as when the sun is from 15° to 20° heloio the horizon the 
rays strike the atmosphere, or clouds, and are bent doion towards the 
earth, producing a little light. Within the tropics the sun sets more 
perpendicularly, hence, speedily. In higher latitudes it sets more 
obliquely, taking a longer time to reach 20°, and thereby causing 
the longer twilight of those regions. 

100. Rainbows.— The semi-circular band or arc, composed of dif- 
ferent colours, appearing upon the clouds during the occurrence of rain 



PHYSIOGRAPHY. 103 

in sunshiue, whicli we term a rainbow, is caused by the refraction 
and reflection of the solar rays in the drops of falling rain. It can be 
only witnessed when the sun is in a certain altitude above the 
horizon — namely, 42° 30' — and when the rain is falling between the 
observer and the part of the sky opposite the sun. The same 
pheoomenon may be witnessed in the case of the spray of cascades 
and loaterfalls. 

There are sometimes two hoivs to be seen, namely, when the light 
is intense, or being sufficiently low in the sky, a second is formed on 
the outside of the first or primary one, by the solar ray entering 
near the bottom of the drops. The rays undergo two refractions 
and two reflections in passing through the drop. The colours in the 
second or secondary one always appear fainter than in the first. 

The Mirage. — The unusual elevation of islands, ships, &c., above 
the surface of the sea, is due to refraction, and occurs when the 
atmosphere is warmer than the surface of the sea. 

101. Temperature is the actual state of a body at any moment, 
determined by a comparison of its magnitude with the heat to 
which it is exposed. A change in temperature is a change in magni- 
tude which the body suffers in the heat to which it is exposed. The 
intensity of heat is measured by an instrument ttrmedi a. thermometer.* 
This consists of a glass tube, hermetically sealed at one end, with 
a bulb at the other containing mercury, which was introduced at a 
certain temperature through the open end, then heated to drive off 
all the air, and afterwards sealed that no air could get in. This 
tube is generally fixed to a hard piece of wood or ivory, on which a 
scale is engraved. This scale has been previously obtained by 
immersing the thermometer in an upright position in melted snow 
or pounded ice, for about half-an-hour, until the mercury has ceased 
to fall, the height of which is then marked on the tube. This is 
the freezing point. The boiling point is obtained by placing the 
thermometer vertically in the steam of pure water until the mercury 
has ceased to rise, when a mark is instantly made. The distance 
between these two marks is then divided either into 212, 100, or 80 
divisions, according v,'hether it is to be a Fahrenheit, Centigrade, 
or Reaumur, The reason mercury is chiefly used in the ther- 
mometer is because of its nearly uniform expansibility under a 
considerable range of temperature. When very low temperatures 
are investigated coloured alcohol is used, it being more able to resist 
congelation than mercury or any other known fluid. 

When the temperature of bodies is raised they, with few excep- 
tions, increase in bulk, this increase arising from the repulsive 
power of heat. Gaseous bodies expand equally for equal increments 
of temperature. Thus 1,000 parts of air at the freezing point 
(32° F.) are increased to 1,365 at the boiling point (212° K.) Mer- 

* Thermo, heat, Mecron, a measura. 



110 



PHYSIOGRAPHY. 



cury in the same range increases from 1 to 1"0019, water to 1-0046 
and alcohol to 1 •0011. It is this expansion and contraction of the 
mercury or alcohol in the thermometers which measures the increase 
and decrease in temperature. 

There are three kinds of graduation. That of Fahrenheit takes 
0° (zero), 32° below freezing point, the boiling point of water being 
212°. In the Centigrade the freezing point is 0°, and the boiling 
point of water ] 00°. In Reaumur they are respectively 0° and 80°, 
In each below 0° is counted with the minus sign. 

Rules. — To convert the degrees of Fahrenheit into those of 
Reaumur : Multiply the niimher of degrees, less 32, ly 4, and divide 
by 9. To convert the degrees of Reaumur into those of Fahrenheit : 
Multiply the given temperature hy 9, divide by 4, and add 32. To 
convert the degrees of Fahrenheit into their Centigrade equivalent : 
Multiply the number of degrees, less 32, by 5, and divide by 9. To 
convert Centigrade degrees into those of Fahrenheit : Midtiply by 9, 
divide hy 5, and add 32. 

102. Heat. — As the atmosphere interferes with the light- 
producing rays, so it does with the rays which produce heat. Though 
the air itself is transparent to heat, the moisture which it contains is 
not, being opaque to it, preventing a large quantity of it from passing 
through to the earth. For it must be remembered, that whatever 
the temperature of the air, it is constantly receiviug moisture from 
the surface of the land and water, thereby causing what we might 
nearly term a second atmosphere. (See "Vapour.") The heat that 
falls on the surface of the earth is partly absorbed and partly 
radiated into the atmosphere. The air through which the heat 
passes is not sensibly heated by the passing of the rays of heat, but 
by conduction — namely, the warmth of the heated earth is commu- 
nicated to the air, the air in its turn communicates heat to the over- 
lying strata of air, and so on. Hence each layer of the atmosphere 
must be cooler than the underlying one, as it would be impossible 
for the earth to make the nearest layer of air as hot as itself, and for 
the nearest layer to make the next stratum of the same heat as 
itself, &c. (For "Average Decrease of Temperature" see 94.) 

103. Winds, or Air in Motion.— Wind is air in motion. As 
there are currents in the ocean, so there are currents in the atmos- 
phere, the cause of which is the unequal distribution of pressure in 
the atmosphere, owing to the unequal distribution of heat and vapour. 
When any portion of the air is heated it expands, and loses its specific 
gravity, thereby causing it to ascend, whereupon a current of colder 
air rushes in to supply the vacancy and to restore equilibrium. In 
this way winds are produced. One of the most notable characteristics 
of winds is their velocity, which varies from a few miles to more 
than a hundred miles an hour — that is, from the gentlest zephyr to 
the most violent hurricane. When it is moving at the speed of 7 



PHYSIOGRAPHY. Ill 

miles an hour it is called a gentle air ; of 14, a ligJit breeze; of 21, a 
good sailing ireeze ; of 41, a gale; of 61, a, heavy storm; of 82, a 
tempest; of 92, a humcane ; and of 100, a violent hurricane, with a 
force sufficient to blow down buildings, tear up trees, &c. 

The following table will give an idea of the relation between the* 
velocity, force, and character of the wind more minutely : — 

Velocity in mUes Force in lb. Avoid.* Common name, 

per hour, per square foot. 

1 -005 Breath of air. 

5 -123 Gentle air. 

10 -496 Brisk wind. 

15 I'll Light breeze. 

20 ,. 1-98 Brisk breeze. 

30 4-5 High wind. 

35 6 Gale. 

40 7-9 Strong gale, 

50 12-5 Storm. 

60 17'75 Great storm. 

80 31 '5 Hurricane or tempest. 

100 49"5 Violent hurricane. 

Winds are classified into three classes, viz., constant, periodical, 
and variable ; but, in whatever class or character they occur, they 
are important agents in the modification and production of climate. 
The most remarkable of the constant or permanent air currents ars^ 
the trade winds and the polar winds. 

104. The Trade Winds, so called from their influence on the 
trade and commerce of the world, are those which prevail within 
the tropics, extending from the parallel of about 30° north and 
south nearly to the equator, forming two zones of perpetual winds, 
the one in the Northern Hemisphere blowing from the TioHh-east, and 
that in the Southern Hemisphere from the south-east. This zone, 
being the highest in temperature, causes the heated or rarified air 
to ascend and flow off as upper currents, travelling towards the poles, 
whilst the colder air from the temperate zones rushes in as under 
cun^ents to supply its place. If it were not for the earth's rotation 
on its axis this colder air would come exactly from the north and 
Bouth ; but owing to the earth's revolution from west to east, and 
that places near the equator move at a much more rapid rate than 
those in the temperate or arctic regions, the air current cannot 
acquire all at once the velocity of that part of the earth over which 
it is advancing, hence it is necessarily left somewhat in the rear ; 
and as it is struck by the objects in that zone with a certain force it 
is deflected in a westerly direction, thereby becoming a north-east 
wind in the Northern Hemisphere and a south-east wind in the 
Southern. 



112 PHYSIOGKAPZr. 

This deflection is caused by the two motions which influence the 
air, namely, (1) a northerly or southerly motion, caused by its ten- 
dency to rush to the equator to supply the place vacated' by the 
heated air, and (2) an easterly motion resulting from the earth's 
rotation. But (Art. 7) the air will not obey either motions or forces, 
taking an intermediate course, namely, in the direction of the 
diagonal of a parallelogram, the sides of which represent the mag- 
nitude and direction of the two forces. 

In the Pacific the north-east trade wind may be said to range 
between the 9th and 25th degrees of north latitude, and the south- 
east one ranges between the 10th and 21st of south latitude. In 
the Atlantic the former is comprised between the 30th and 8th 
degrees of north latitude, and the latter within the 3rd of north and 
the 2Sth of south latitude. These limits, however, vary, advancing 
with the sun. Thus at the summer solstice the region of the winds 
is entirely carried north of the equator, and at the winter solstice ifc 
is carried considerably south, but not entirely passing the equator. 
The reason it goes farther north than south is owing to the greater 
quantity of land in the Northern Hemisphere. Of the two the 
trade wind in the Southern Hemisphere is the stronger and more 
constant. Their regular rate is from 10 to 20 miles per hour, but 
on approaching the continents their courses are interrupted by the 
unequal heating of the land and water surfaces. Hence within 
these coast areas, instead of currents being perennial, they assume a 
periodical character, and as they approach the equator of tempera- 
ture their currents begin to abate, thereby producing the region or 
'belt of calms, as they are termed. There are also other belts of 
calms, each formed where the winds cross, as the belt of calms of 
Cancer (sometimes called the horse latitudes) and the belt of calms 
of Capricorn, when the trades and anti-trades, as these westerly 
winds are called, interchange. 

105. Periodical Winds. — The most important of this descrip- 
tion are — 

(1) The monsoons, which are modifications of the trade winds 
(or trades as they are called), being due to the presence of vast 
masses of territory. They are termed monsoons, or season winds, 
because they change their course with the seasons, blowing from one 
part of the earth for one-half of the year, and from the opposite part 
for the other half. From April to October they blow from the 
south-west, and from October to April from the north-east. 
They prevail chiefly in the Indian Ocean, extending to the north and 
east of Australia into about 14° west longitude. When the sun is 
north of the equator the large continents of India and China are 
heated to a very great extent, heating the surrounding air, which 
rises, and the south-east trade rushes in to fill the vacant space ; bub 



PHYSIOGRAPHY. 113 

owing to the rotation of the earth and other local causes, it is 
deflected, becoming the south-west, south, south-east, or east monsoon 
on different parts of the coast. Similarly, when the sun journeys on 
to the Southern Hemisphere, the wind follows, and causes what is 
called the south-east monsoon, blowing from October to April, 
though this is really the ordinary north-east trade wind. At the 
changes from one to the other in April or October — a period known 
among mariners as the hreakirvg up of the monsoons — furious storms 
of wind, rain, and thunder occur, owing to the two opposite air 
currents contending for the mastery. There are other parts in which 
the monsoons occur, as on the West Coast of Africa, the coast of 
Brazil, the coast of America from California to about 45° south 
latitude, &c. 

(2) Land and Sea Breezes prevail on almost every seaboard, but 
more particularly in the tropics, where they occur regularly. The 
land breeze sets in dnring the night, and the sea breeze during the 
day. They owe their origin to the unequal temperature of sea and 
land by night and day. Thus, during the night the land loses its 
heat by radiation more rapidly than the sea ; hence the cool air 
from the land flows to the sea, to take the place of the warmer air 
and thus forms the land breeze. In the daytime just the opposite 
occurs, as the cool air flows from the sea towards the land and 
creates the sea breeze. To many islands they are of great import- 
ance, as by their influence they are kept cool and inhabitable. 

106. Variable Winds. — With the exception of the winds above 
enumerated there are many which are very variable, still they are 
obedient to law and law-directed forces ; but these forces being so 
comphcated they are not, comparatively speaking, so well under- 
stood. There are two winds in the Northern Hemisphere which 
may be considered the prevailing winds — namely, that of the north- 
east, being the cold polar one on its journey to the pqiiator, and that 
of the south-west, being the warm equatorial currents hurrying to 
the poles ; and similar in the Southern Hemisphere. All other winds 
are local, depending on local circumstances, a few of which we 
will just briefly mention. 

Hot Winds. — The chief of these are those that originate in the 
Great Desert of Sahara, and they go by several names, but are 
generally called the simoom.* In Turkey they are called samiel; 
in Egypt, khansin (fifty) ; in Italy, sirocco ; in Spain, the solano ; 
and in Guinea and Senegambia, harmattan. The simoom is 
an intensely hot, suffocating wind, laden with fine particles of 
sand, often causing destruction to the whole caravan of men and 
animals. The only way to escape its effects is to lie prostrate 
on the ground, with the face buried in the sand, till the violence 

♦Arabic, hot, ;piisonous. 



114 PHYSIOGRAPHY. 

of the blast is passed. The fohn is the name given to the hot winds 
that occasionally blow over Switzerland. 

There are other winds just the reverse of these — namely, cold 
piercing ones — such as the puna, pampero, lora, mistral, &c. The 
puna is so called from originating in the upland of Puna, sweeping 
over the Plateau of Peru for about one-third of the year. The 
pampero is a violent west wind, which passes over the pampas of 
Buenos Ayres. • The iora, blowing north-east from the Alps, in 
Istria and Dalmatia, is at times very violent indeed, overturning 
both men and horses at the plough. The mistral is a violent north- 
west wind, blowing down the Gulf of Lyons, acd felt chiefly in the 
south-east of France. The etesian* winds are those which prevail 
very much in early summer all over Europe. 

107. Storms are sudden and violent commotions of the atmo- 
sphere. All great storms are found to partake of a circular motion, 
though the diameter or whirl is often hundreds of miles in extent. 
Those needed to be mentioned here are cyclones, typhoons, tornadoes, 
hurricanes, and whirlwinds. 

Cyclone is the name applied by navigators to those rotatory 
hurricanes which most frequently occur between the equator and 
the tropics, and near the calms of Cancer and Capricorn. They 
sweep round and round with a progressive motion, describing a 
curve, rotating in both hemispheres in a contrary direction to the sun. 
In different regions they are known as tornadoes, whirlwinds, typhoons, 
and hurricanes, being called hurricanes or tornadoes in the West Indies, 
where they are most frequent about the time of the equinoxes, and 
also in the Indian Ocean, extending from Madagascar nearly to 
Australia, and from 4° to 35° south latitude, occurring here at the 
change of the monsoons. In the Chinese region they occur about 
once in three years, generally from June to November, extending 
from the Ganges to Japan, and from latitude 5° N. to 25° jST. They 
are here called typhoons. The tornadoes of the West Indies and the 
Indian Ocean are generally accompanied with thimder and lightning, 
and sometimes showers of hail. 

It is worthy of note that in the tropical climates the barometer 
indicates the approach of a hurricane, the mercury in the tube being 
depressed or agitated in an extraordinary manner for some time 
before any signs of a storm appear in the horizon ; also during 
the first half of the storm the barometer falls, and during the last 
half it rises. This is owing to the density of the air increasing from 
the centre to the circumference of the storm, so that when a 
hurricane passed diametrically over a district the pressure would 
decrease, but gradually increase during the last half of the storm. 
The direction the centre of the storm lies may be always found by 

•Greek, er^atos, annual. 



PHYSIOGRAPHY. 115 

standing with, the hack to the -wind, then in the Northern Hemisphere 
the centre is towards the left hand, and in the Southern Hemisj)here 
to the right hand. This rule is of importance to mariners, showing 
them how to steer so as to get out of the cyclone. (For " Thunder," 
and "Magnetic Storms," see 30, 31, 35.) 

VAPOUR, EVAPORATION, AND CONDENSATION. 

108. Evaporation is the conversion of a fluid into vapour. It 
is produced by the solar heat, which raises water into the atmosphere 
in an invisible form. Familiar examples of this may be noticed in 
the drying of wet clothes which are hung out in some open place, 
and watered streets beginning to dry nearly as soon as watered, &c. 
At all temperatures water evaporates, even if it is ice. The rate at 
which evaporation takes place depends upon (1) the temperature, the 
higher the temperature the greater the evaporation ; (2) the amount 
of vapour in the atmosphere, as a certain quantity of air can only 
receive a certain quantity of vapour, after which it is said to be 
saturated, or to have reached the point of saturation ; though it must 
be remembered that the higher the temperature the more vapour 
will the air be able to contain before reaching this point of satura- 
tion ; hence the amount of vapour in the air depends solely on its 
temperature. From this we see that the evaporation is greatest in 
the torrid zone, it being estimated that on an average 16 feet depth 
of water is raised annually from the surface of the sea in these parts. 

109. Condensation. — Dew. — As heat evaporates water and 
causes it to ascend as vapour, cold, or a decrease in temperature, 
causes it to condense, forming dew, clouds, rain, hail, snow, &c. 
Thus, after sunset the earth and air lose the heat they have received 
from the sun during the day by radiation into space ; but the earth, 
being a good radiator, parts with it more rapidly, thereby causing 
the moisture in the air to be condensed on the earth's cool surface, 
forming dew. The temperature at tvhich dew begins to he deposited is 
termed the dew-point, and it varies according to the saturation of the 
air. It may be noticed that some substances have dew on them 
while others remain dry. This is owing to the latter being bad 
radiators and the former good ones. Dew is never deposited in 
dull cloudy weather. The conditions favourable for its formation are 
an unclouded sky and a calm night preceded by a warm dry day. 
On a windy night the radiation would be disturbed, and thereby cause 
the moisture to be evaporated as soon as formed. Tropical countries 
favour these conditions, hence the deposition of dew is most copious 
there, compensating in a great measure for the absence of rain in 
these parts. In the British Isles dew is heaviest in spring and 
autumn. 



116 PHYSIOGRAPHY. 

Hoar Frost is simply dew in its frozen state. The chilling effect 
of radiation reaches but a short distance above the ground, as at two 
or three inches above the ground it is only about one-half, and at six 
feet only about one-twentieth. Generally the body itself is about 
4° below the temperature of the air just above it. 

Fog and Mist. — Fogs result from currents of moist air coming in 
contact with the colder surface of the earth, the moisture being 
condensed into the visible form of fog or mist appearing near the 
surface of the earth. Mountain sides, river valleys, sea coasts, and 
cold countries favour the formation of fogs, owing to the unequal 
temperature of the contiguous lands and waters. According to 
Kaemtz, fogs may be expected frequently where the soU is moist and 
hot and the air moist and cold. Those occurring in Newfoundland 
are occasioned by the warm waters of the Gulf Stream being con- 
densed by the cold air of the arctic current. 

110. Clouds are masses of aqueous vapour in a partially con- 
densed state, differing from fogs in being condensed at a greater 
elevation, though they are not so high as they appear, as a traveller, 
, for instance, on a mountain may often see clouds floating beneath 
him. The average height of the clouds is between one and two 
miles ; streaky-curling ones, like hair, are often five or six miles high, 
the nearest to the earth being those highly electrified. In this 
covmtry the height is from 2,000 to 6,500 feet, with a thickness of 
from 2,000 to 3,000 feet. The speed at which clouds move is much 
greater than appears, owing to their height, as they often move 
at the rate of from 70 to 100 miles an hour. 

Classification. — Clouds are grouped into seven classes — there 
original, and four compound forms arising from combinations of the 
others. They are : — 

Original. — (1) Cirrus, or curl cloud. (2) Cumulus, or summer 
cloud. (3) Stratus, or fall cloud. 

Compound. — (4) Cirro-cumulus. (5) Cirro-stratus. (6) Cumulo- 
stratus. (7) Nimbus, or rain cloud. 

(1) Cirrus clouds appear like fibres, loose hair, or thin streaks. 
They are the most elevated of all, being not less than three, and 
often reaching six, and even ten miles in height. They have a 
tendency to arrange themselves in parallel or divergent bands. At 
the equator these extend from north to south, but in higher 
latitudes, as in this country, they stretch from north-east to 
south-west, varying from that to north-west and south-east. They 
are supposed to consist of vapour below the freezing point, as minute 
ice crystals, or pure snow flakes. 

(2) Cum.ulus clouds appear in great masses, like volumes of smoke. 
They are formed after sunrise, gradually increasing and ascending 
higher as the day advances, disappearing towards evening. If they 



PHYSIOGRAPHY. 117 

increase in size at sunset a thunderstorm may be expected in the 
night. 

(3) Stratus (or FaM Cloud) is a kind of heavy layer of mist or 
vapour, especially prevailing on a summer evening, rising at sunset 
or nightfall in low damp places, and vanishing at the approach of day. 
This is the nearest to the earth of all the clouds, and is closely allied 
to fogs and dew, being formed by the vapours rising from the earth 
as it cools by night. 

The cirro-cmnulus, cirro-stratus, and cumulo-stratus, as their 
names signify, are merely combinations of the original three. The 
Nimbus (or rain cloud) is of a greyish appearance, with fringed 
edges. It is formed from any of the others, except the cirrus, and 
is always low down, mostly between 1,000 and 4,000 feet from the 
earth. 

111. Kain is vapour condensed in the air and precipitated to th? 
earth in showers, the condensation being caused by a considerable 
diminution in temperature. As long as a cloud remains where the 
temperature is sufficiently high it is capable of containing its mois- 
ture, but should it get carried by the wind into a cooler region it 
is unable to do so. Condensation then sets in, and the several vesicles 
of vapour uniting cause the weight to become too great to be 
supported by the air. Hence the drop thus formed falls to the 
groimd. 

Rainfall. — By the time the north-east and south-east trades meet, 
producing the equatorial calms, the air is heavily laden with vapour. 
Having travelled in each hemisphere over a very large space of the 
ocean, it now ascends, expanding and.- becoming cooler, part of the 
vapour thus condensed coming down as rain. It is thus that we 
have a region of constant rain at these calms. The nearer we 
approach the poles the less rain descends. The quantity falling 
in any cotmtry depends on its nearness to the ocean or other large 
bodies of water, upon the temperature, upon the seasons, and upon 
the direction of the prevailing winds. The coasts of a country, 
or those coimtries where the winds blow chiefly from the sea, 
receive a greater proportion of rain than the interior. Chains of 
hills also affect the air much by coming in the way of the winds and 
causing them to descend. Hence the amount of rainfall depends in a 
great measure upon whether the country is moimtainous or not, and 
also on the direction of the mountains. Thus, for instance, the most 
remarkable rainfall in the world occurs at Cherrapoonjee, in the 
Khasyah Mountains, its annual average being 499' 3 inches, though 
in some years its rainfall has exceeded 600 inches. This extraordinary 
downfall is attributed to the abruptness of the mountains which face 
the Bay of Bengal Another good example is furnished even in our 
own country, where the warm winds of the Atlantic meet the hills and 
mountains of the west side, especially in the Cumbrian Hills, where — 



118 PHYSIOGRAPHT. 

namely, at Scathwaite — the average is 145*1 inches, the west side 
entirely averaging 45 inches, and the east coast only 27 inches. A 
similar example is to be found on the west coast of Ireland. The 
mean annual average for Great Britain is 34 inches, and England a 
little over 30 inches. The reason that the east side does not receive 
so much rain as the west is self evident, namely, that the mountains 
on the latter side condense the warm moist winds of the Atlantic, 
partly preventing their passage over, rain coming down in torrents, 
and the air which does reach the other side is thus comparatively dry. 

In Guiana, Brazil, and North and West India, the average rainfall 
exceeds 300 inches. 

When it is stated, as above, that the mean annual rainfall of a 
place is 30 inches, it implies that the amount of rain that falls in the 
course of a year would on an average cover the ground to a depth of 
that number of inches (30), supposing the ground perfectly level and 
the water neither to sink into the earth or evaporate. The instru- 
ment used for the measurement of rainfalls is called a rain gauge. 

SPECIMEN TABLE OF AVERAGE ANNUAL EAINFALLS OF A FEW PLACES. 

Names. Inches. 

CheiTapoonjee 499"3 

Vera Cruz (Mexico) 278 

Akyab (Arracan Coast) 204 

Andes (Patagonia) more than 200 

Scathwaite (English Lake district) 1 45 '1 

Glencroe 1277 

Bombay 76*2 

Calcutta 66 

Keswick (Cumberland) 63 

Cahirciveen (Ireland) 59'4 

Kendal 58 

Madras 56-3 

Glasgow 43-3 

Manchester 35*5 

Cork 35-5 

Lisbon 27'5 

London 24*2 

Paris 199 

Generally speaking the greatest rainfall is in the tropics, and 
gradually decreases as we journey towards the poles. At the tropics 
its annual average is about 95 inches, but in the frigid zone it is 
only about 15. As the rain depends much on the wind it seems to 
follow much the same arrangement, namely, periodical in the tropics, 
variable in the higher latitudes, and abnormal in certain districts, 
when it occurs either in excess or is altogether absent. In the tropica 
the rainy season commences at the changing of the monsoons (p. 113). 



PHYSIOGRAPHY. 



119 



In general terms, more rain falls from April till October than in the 
other months, especially in the northern half of the torrid zone, 
where the wet season occurs at this time, the dry season commencing 
in October and continuing until April. In the southern half this 
order is reversed, the dry taking the place of the wet. 

Rainless Districts. — There are some places where little or no rain 
ever falls, the principal of which are the Sahara Desert, the great 
deserts of Arabia, Persia, Mongoha, including Gobi, Thibet, &c., 
and North Mexico and west of Peru, in America, forming as it were 
one continuous area, varying in tread th from the 15th to the 47th 
parallel, and in length from 16° W. to 118° E. longitude. The least 
rainfall in the world of which we have record is at Suez, being 1"3 
inch. The area of these rainless regions is about 5^ million square 
miles. 

112. Snow. — "When the temperature of the air is below the 
freezing point — namely, 32° F. — the condensed vapour must be in the 
form of particles of ice ; hence when they fall to the earth we have 
snoio instead of rain, and these frozen particles uniting together form 
flakes, the size of which depends upon the amount of moisture and 
the extent of the prevailing low temperature. Sleet is formed by 
the flakes in their descent encountering warm strata of air. Snow 
is generally composed of crystals in the form of six pointed or 
angled stars of 60°. As many as 1,000 different kinds have been 
noticed. 













Snow Flakes magnified. 



120 



PHYISOGRAPHY. 



Snow-line. — At places within the tropics at the sea level, and for 
15° or 20° beyond in either hemisphere, snow never falls, the 
reason of which is obvious, 
only falls during winter and at 



considerable elevation ; but in 
the polar regions, and at extreme 
heights in all latitudes, it 
becomes constant. This limit is 
termed the snow-line, the height 
of which varies not only with 
the latitude, which descends 
constantly as we travel towards 
the poles, but also with the 
situation as regards exposure to 
the sun and rain-bearing winds, 
the degree of humidity of the 
climate, and other causes. The 
following diagram gives a 
general idea of 
equator, down to the level of the 



Also in the higher latitudes it 
ikoOD 




(J, 10.20 20 LO 50 60 10 ZO qOt 
Fig. 12. 
its gradual descent from 16,000 feet 



at the 
at the poles. But it 
must be understood that it does not always follow this rule, as 
for instance, on the south side of the Himalayas the snow-line 
is about 4,000 feet higher than that on the north side, owing 
chiefly to the great dryness of the enormous tablelands of 
Central Asia, as they increase the radiation of the solar heat, hence 
the evaporation, and also to the moisture conveyed to the south 
side by the warm winds of the Indian Ocean. The highest point to 
which the snow-Une reaches is about 18° degrees south of the 
equator, namely, in the Andes of Bolivia, where it exceeds 20,000 
feet. 

HEIGHT OF SNOW-LINE IN DIFFERENT LATITUDES : — 



North 
Latitude. 

Spitzbergen 78° 

^North Cape 71 

Suhtelma (Norway) 67° 

Oonalaska 53^ 

Altai 50° 

Alps 46° 

Caucasus 43° 

Eocky Mountains 43° 

Pyrenees 42f° 

Etna 371° 

Himalayas (North) 29° 

Himalayas (South) 28° 

Purace (Andes) 21° 



Height 

in feet. 



2,400 

3,850 

3,500 

7,030 

8,890 

11,060 

12,470 

9,000 

9,750 

19,000 

15,000 

15,380 



PHYSIOGRAPHY. 121 

South Height 

_ Latitude. in feet. 

Andesof Quito ^ 0° ... 15,705 

Kilimanjaro 4° ... 17,000 

Andes of Bolivia 16° ... 17,700 

Andes of Bolivia 18° ... 20,060 

Straits of Magellan 63^° ... 3,540 

South Georgia 54^°... 

From the above it will be seen that the greatest change in the 
snow-line takes place between 30° and 60°. 

Hail is supposed to be formed in the higher regions of the atmo- 
sphere. It consists of snow coated with ice frozen to it in its 
descent to the earth. It may briefly be defined as frozen rain. It 
occiu's in all latitudes and at all seasons. It appears to be con- 
nected in some way with the electricity of the atmosphere, thunder- 
storms often occurring while hail is falling. Hailstones are usually 
pear-shaped, and small in size, but have been known as large as 
hen's eggs. Hailstorms occur mostly in summer and in the day- 
time, and most frequently near mountains, seldom occurring in low- 
land plains within the tropics, but common at several thousand feet 
of elevation. 

Ice is frozen water, or water that has been crystallised by the 
atmospheric temperature being below or at 32° ; for salt water 4^° 
lower. On close examination it will be found to consist of six- rayed 
stars, like the characters of snow, and to be of pure water. (For 
"Expansion," &c., see 45.) Ice has, through some circumstance 
or other, been formed at the bottoms of rivers and ponds — called 
ground ice. Occurrences of this description have been noticed in 
the Thames, and also in the rivers of Siberia. 

Avalanches are accumulations of snow, or snow and ice, which 
frequently roU with great violence from lofty mountains — as the 
Alps for instance — ^into the valleys or plains below, carrying destruc- 
tion and ruin. There are three descriptions. (1) The wind 
or dust avalanches, that is, fresh-fallen snow carried down into the 
valleys in the form of dust. They are very light — ^hence not so 
destructive. (2) Mountain, snoio, hail, or thunder avalanches. These 
fall by their own weight, carrying with them the ground on which 
they lie, together with trees, rocks, &c., and mostly occur in spring. 
(3) Earth avalanches, or landslips, when they occur, are by far the 
most destructive. The earth, having been weakened by much con- 
tinuous rain, slides down into the valleys with everything upon it, 
houses, trees, and even entire forests. 

113. Glaciers are enormous masses of ice, formed on mountains 
above the snow-line, which creep down into warmer regions, where 
they melt and disappear, giving rise to streams, as, for instance, the 
Rhine and Rhone from the glaciers of the Alps. In mountain gorges 



122 PSYSIOGRAPHT. 

they descend as ice streams, the ice being partly plastic, though in 
appearance rigid. It differs also from ordinary soUd ice, being of a 
blue-veined structure, due to great pressure. These streams of ice 
travel at the rate of from 16 inches a day in winter to about 30 in 
summer, and follow the same laws as rivers of water — the velocity 
being greatest in the centre. The glacier, in its journey over rocks, 
&c., often causes great cracks or clefts of great depth, called crevasses, 
and tears away the loose rock and debris, which it carries with it, 
depositing these moraines,* as they are termed, when the glacier melts 
away at the snow-line, beginning to flow then as streams of water. 

Glaciers are most abundant in the Alps, Himalayas, Norway, New 
Zealand, and continually in arctic and antarctic regions. 

The most extensive occur in Greenland, some of which are 45 
miles broad and from 350 to 500 feet in height. Large ones also occur 
in the Himalayas, the Rocky Mountains, Iceland, Spitzbergen, &c. ; 
but the most remarkable are those of the Alps, where over a thou- 
sand distinct glaciers occur. Some of the chief are Mer-de-Glace, 
with an area of 18 square miles, and the Glacier-de-la-Brenva, both 
in the Mont Blanc group ; the Zermatt Glacier, in the Monte Rosa 
group ; and the Great Aletsh Glacier, with an area of 34 square 
miles, in the Oberland group. 

114. The Action of Rain, Springs, Rivers, Snow, and 
Glaciers on the Earth's Crust. — The action of these agents 

upon the crust of the earth is termed sub-aerial'f denudation. 

Rain. — Part of the rain which falls on the surface runs off in 
brooks and rivers. Another part percolates through the ground 
until it meets a less pervious rock, where it forms a reservoii-, or 
escapes through the sides of a hill, &c., forming springs. (See 87.) 
It is to the effect of rain that landslips may be attributed. The 
water, soaking through the ground, accumulates on a bed of clay, or 
some such stratum, and loosens the cohesion between it and the upper 
beds, when, if the strata are favourably placed, it may happen that 
the upper layers will slide over the slippery clay in which the strata 
are inclined. The rainwater which flows over the surface continually 
sweeps with it the minute particles of sand, rock, &c., which the 
action of the weather has loosened. 

Rivers. — Streams in their course through hilly regions wear 
channels for themselves, and carry along with them the displaced 
materials. (See " Deltas.") They have generally a tendency to wind 
about, in many cases a great number of convolutions occurring in 
the space of a mile or so. The reason of these tortuous courses may 

* These moraines are called lateral when they Hue the sides of the glacier ; 
terminal when they are deposited in heaps at its extremity ; and medial when 
two glaciers join, causing the inside moraine of each to unite. 

t Sub, under. Aer, the air. 



PHYSIOGRAPHY. 123 

be attributed to tlie operation of the natural law, that a mass of 
matter in motion has a tendency to move in a straight line. (Also see 88.) 

Frost. — TVlien water gets into tlie joints and crevasses of a rock, 
and then becomes frozen, it expands, forcing apart the blocks and 
particles, so that as soon as the thaw comes the loosened par- 
ticles and pieces fall asunder. Snoio also is at times a disintegrator 
of rocks — namely, when accumulated on mountains and sliding 
down as avalanches. Glaciers, in their motion over rocks, exert great 
erosive powers, and (not like water, dividing on meeting an obstacle) 
push everything before them that gets in their way. By this means all 
loose stones in the bed of the glacier are torn up, making it a smooth 
undulatit g surface, with scratches or furrows running parallel with 
the stream of ice, caused by angular fragments of rock, which have 
fallen through crevices from the surface of the glacier, being dxagged 
along with the weight of the ice above them. 

115. Phenomena of the Arctic and Antarctic Regions. 

The Arctic Regions are the high latitudes surrounding the North 
Pole, and the Antcuctic the regions surrounding the South Pole. As 
they are the farthest from the equator they are the coldest regions 
of the world, being inaccessible to man beyond the 84th parallel of 
latitude. The highest point ever reached is 83° 20' 30", and that 
by the arctic explorers of 1876, under Captain Nares, namely 
Commander (now Captain) Markham and Lieutenant (now Com- 
mander) Parr, with 15 men under them. The Alert, one of the 
vessels under Captain Nares, also reached a higher latitude than had 
ever previously been reached by a vessel, namely, lat. 82° 24'. The 
temperature during the winter months is so low that mercury is of 
no use in the thermometers to measure the cold, as it becomes frozen, 
remaining so for more than a month at a time. Spirit thermometers 
were used, showing a temperature of — 74°, or 106° below the freezing 
point, in March, though the thermometer may register, during the 
summer monthes, a temperature nearly equal to the mean of the 
tropics. The seas of the polar regions are closed during the greater 
part of the year, being only open for a few months in summer. The 
extent to which the Arctic Ocean is frozen is not known. At a 
degree of latitude varying with the season of the year, ships are 
barred from going northward by a barrier of frozen ice. The outer 
edge of this barrier gets spUt and broken off into vast mountains of 
ice during the summer, commencing at the latter end of April, 
drifting towards the south. The largest of these ice mountains are 
formed from the glaciers of these regions, which spread almost over 
the entire surface, gliding on as rivers of ice till they reach the sea 
shore, and there, losing their support, the front parts break off, and 
float away as icebergs (ice mountains). Some of these bergs are 
several miles in circumference, and from 50 to 250 feet above the 



124 PHYSIOGRAPHY. 

surface ; hence the entire thickness of the greatest are 250 X 9 = 
2,250 feet, the specific gravity of ice being "9 and water 1. In the 
Atlantic icebergs from the arctic regions have been carried by the 
polar current as far as the 44th parallel of latitude, and from the 
antarctic they have reached the Cape of Good Hope. The ice that 
forms on the surface of the sea is called field ice. It forms in the 
winter and breaks up in the summer. A small field is termed 
an icefloe, and one much broken up forms a pack, or pacJc ice. 

Bed Snow in the Arctic Regions. — Red snow is a phenomenon 
which is often observed in the polar regions. Captain Ross dis- 
covered on the shore of Baffin's Bay a range of cliffs extending for 
more than eight miles covered with a brilliant red snow, in some 
places 12 feet deep. The cause of this appearance has been found 
to be due to the presence among the snow of a very minute plant, 
which Sir William Hooker named Palmella nivalis. This snow has 
also occasionally been met with in the Alps and in Scotland. 

Day and Night in these Regions. — As we approach the poles the 
inequahty between the daj'S and nights becomes greater and greater, 
until at the poles themselves a day of six months alternates with a 
night of the same duration. The most distant parallels that the 
sun describes north and south of the equator are 66^° from the 
latter, and 23^° from the poles. Hence when the sun is in the 
tropics all the polar circle in that hemisphere will be within the 
illumination of the sun, as it will be with 90° of that luminary. 
During the same time the other polar circle will be in darkness. 
Therefore during the year they have one day of exactly 24 hours 
and one night of similar length. 

The change from short days to long ones, and vice versa, in these 
regions takes but a very short time. We may fancy that during 
the six months that the sun is absent there would be total darkness, 
but such is not the case, owing chiefly to the reflection of the sun, 
namely, tvMight, which in these regions lasts for months — at the 
north pole from September 22nd to November 12th, and from 
January 25th to March 20th. Besides the twilight there are the 
stars, and also the snow on the ground, which mitigate the darkness, 
the moon also appearing every 14 days. Very few animals or birds 
inhabit these parts. A few musk oxen, hares, and ptarmigans reach 
as far as latitude 82°. 

One or two geological facts regarding the arctic regions have been 
brought to Hght by the late expedition, bearing on the changes in 
the climate of those regions. Miocene beds, including a thick seam 
of coal, were found to exist as far north as latitude 81° 44'. The 
shales and limestone of the same formation contain abundant 
examples of the flora (flowers) of that epoch, thereby proving that 
at a comparatively recent geological period there existed a temperate 
climate within 500 miles of the north pole ; and according to Mr. 



( 



PHYSIOGRAPHY. 125 

C. Markham excellent coal was found in latitude 82"*, and impressions 
of leaves, &c., were brought back, showing that luxuriant forests 
had grown within 450 miles of the pole. Wood has also been dis- 
covered in the now frozen regions, with the harh on, having evidently- 
grown where found, thereby showing that there must have been 
great and rapid changes of climate in a comparatively short period in 
the polar region ; and the only way we can account for this is a 
change in the inclination of the earth's axis. 

The Antarctic Ocean has not been explored so high in latitude as 
the Arctic, the highest latitude reached being 78° 15', in 1841, by- 
Sir James Ross. It is supposed that nearly- the entire area, 
embraced by the antarctic circle, is occupied by land, covered con- 
tinually with snow. Two volcanoes exist, if not more, in these 
regions — Mount Erebus, 12,400 feet above the sea level, and Mount 
Terror, about 9,000 feet, the former is in a state of constant 
activity, and the latter extinct. 

The cold is more severe than in the arctic region. For instance, at 
lat. 64° S., Captain Nares found the temperature of the atmosphere 
to be 65' below freezing point (31"5°) in February, which is lower 
than the temperature of the arctic region 10° nearer the pole. 

CLIMATE, AND CAUSES AFFECTING IT. 
116. Under the term " Climate " we speak of the general 

weather conditions of any district, as mild, or severe. 

Climate depends on numerous circumstances, the chief of which 
are — (1) Latitude. (2) Altitude. (3) Nearness to the sea. 
(4) Distribution of land and water. (5) Mountains. (6) The pre- 
vailing winds and ocean currents, &c. The priaciple cause affecting 
climate is the latitude, so that we may say generally that the climate 
of a place is warmest the nearer it is to the equator, or that its 
temperature diminishes in proportion as its latitude is greater, or 
more correctly in proportion to the square of the cosine of its lati- 
tude. The second principal cause is the altitude. (See " Snow-line," 
and "Height and Pressure of the Atmosphere," 112, 94.) Thirdly, 
its nearness to the sea, depending upon the unequal reception and 
radiation of heat by land and water. The heat falling on the land 
is partly absorbed and conducted downwards into the soil, and 
partly radiated into the atmosphere. The greater part of that con- 
ducted in the earth (which never sinks more than 70 feet, and for 
practical pm-poses may be regarded as within a few feet of the surface) 
is given off by night, but the remainder accumulates day after day all 
throiTgh the summer, keeping it in store to return to the atmo- 
sphere in winter. On the other hand, the rays of heat falHng on the 
water are much more readily absorbed, and also radiate more slowly. 
Hence, there will be a much greater store of heat accumulated in 
the waters of the ocean during summer than in the earth, so that it 



126 PnYSIOGRAPHT. 

will have a great deal more heat to return in the winter than the 
earth. It is owing to this that islands and seaboards have more 
equable climate than those in the inside of a continent. For 
instance, contrast the climate in winter of any place in England with 
that of any place in the same latitude in Russia ; or, again, the 
comparatively cool summers and mild winters with the interior of 
Germany, which experiences excessively hot summers and cold 
winters. Such places as the British Isles, New Zealand, &c., are said 
to possess an insular climate, and the interior of Germany, Russia, 
&c., continental. 

The prevailing winds and ocean currents also exercise great 
influence on the climate, as they may be either cold or warm, &c., 
especially in the case of the Gulf Stream, and the arctic and antarctic 
currents. The former, carrying warmth and moisture, lessens the 
winter climate of the west side of Europe, while the arctic current 
brings cold, tempering the summer climate of the eastern part of 
North America. The direction of mountain chains and the cultiva- 
tion of a country also influence the climate. 

Representation of Climate. — From the above considerations it will 
be seen that the parallels of latitude do not represent the belts 
of corresponding climates. So that places having the same summer 
temperature may readily be known, long seiies of observations 
have been taken, and lines of equal heat, called Isotheral Lines, have 
been drawn, showing these places at a glance. In a similar manner, 
lines are drawn through places having the same winter temperature, 
these are called Isocheimal Lines. Lines drawn through places having 
the same mean annual temperature, are called Isothermal Lines. 
(See map.) From the map it will be seen that the line of greatest 
heat does not coincide with the equator but hes north of it, from 
about 150° west longitude, across both hemispheres, falling below 
it in the island of Borneo. The average temperature of the line ia 
about 84° F., being hottest near the Red Sea. Lines drawn through 
places having the same mean barometic pressure are term|d isobaric 
lines. 

CHmates are generally grouped into three classes. (1) Those in 
which the temperature of summer is but little in excess of that of 
winter, called insular chmates, as in this country. The mean difler- 
ence between summer and winter here is only about 20°. (2) Those 
in which the difference between summer and winter is strongly 
marked, owing to their distance from the sea. These are termed 
continental. Central Russia and Germany, in the same latitude as 
England, have a range of 86°. (3) Those in which the difference is 
very great. For instance, in Siberia the difference amounts to 106°, 
the summer temperature being 62'2°, and the winter- 43'S°. These 
are termed extreme chmates. Also, regarding the distribution of 
the climate, there is one fact not to be lost sight of, and that is — the 
Northern Hemisphere is about 3|° warmer than the Southern one, 
owing to the much greater extent of sea to the south. 



MAP OF ISOTHERMAL LINES. 



127 




128 PHYSIOGRAPHY. 

LIFE AND ITS DISTRIBUTION. 

117. Under the term "Life" is embraced all that appertains! to 
the vegetable and animal kingdoms, subjects which really belong to 
Biology* (Botany and Zoology). The part to be noticed chiefly, in 
the elements of Physiography, is their dependence on climate and 
other conditions regarding their distribution. 

In speaking of animals and plants we group together those forms 
which possess much in common as genera. These we split up into 
species, and, for the sake of brevity, the term flora is used to 
designate the plant life of a region or epoch, smA fauna to designate 
its animal life. The area within which a given plant prevails is 
called its habitat, or area of distribution. Plants are divided into 
two classes, namely, cryptogams, or non-flowering plants, embracing 
ferns, mosses, lichens, seaweed, fungi, &c. ; and phenogaras, or 
flowering plants, as the pine, chestnut, maple, spruce, &c. The 
number of species known is about 130,000, six-sevenths being 
flowering plants and the remaining one-seventh non-flowering. It 
is calculated that there are upwards of 220,000 species existing on 
the earth. 

118. Distribution of Plants according to Climate.— The 

surface of the globe has been divided into eight zones, bounded by 
isothermal lines, or mean temperature. (1) The equatorial zone, or 
region of palms and bananas, bounded by the isotherms of 79"3° F. 
on each side of the equator. This zone contains the greatest variety 
of species and the most luxuriant, the principal of which are the 
palms, banyans, breadfruit trees, bamboos, orchids, arborescent 
grasses, &c. (2) The tropical zone of tree-ferns and figs, between the 
isotherms of 79'3° F. and 72*5° F. each side of the equator. Besides 
the ferns and figs, &c., many equatorial plants are found, as well as 
cofiee, cotton, pineapples, sugarcanes, cinnamon, logwood, indigo. 
(3) The sub-tropical zone of laurels and myrtles, between 72'5° F. and 
68° F. (4) ^}ie ivarm temperate zone, or region of evergreens, hetween. 
68° F. and 54"5°F., also includes oaks, figs, chestnuts, olives, oranges, 
the vine, pomegranates, and many other sub- tropical forms ; of 
grain the chief is wheat. (5) The cool temperate zone of deciduousf 
trees, between 54:'5'^ F. and 41° F. This zone includes all English 
trees and plants, and beyond it the cultivation of wheat does not 
extend in the Northern Hemisphere. (6) The sub-arctic zone oj 
coniferous trees {pine, larch, spruce, juniper, <tc.), between 41° F. and 
36 "5° F. In the Northern Hemisphere it is the zone of firs and 
willows, and in the Southern it embraces a few barren islands. 
(7) The aixtic zone of the birch and pine in the Old World and the 

* Bios, life. Logus, a discourse. 

t Trees which cast their leaves in winter. 



PHYSIOGRAPHY. 129 

rJiododendA'ons in the New between SS'S" F. and 41° F. This zone 
is marked by the dwarf birch, alder, and willow, few pines and firs, 
and by grasses, and numerous lichens and grasses in the north. 
(8) The folar zone of lichens and mosses (cryptogams), between the 
mean summer temperature of 41° and 36*5° F. In this zone there 
are no trees nor bushes, nor any cultivation of plants for food. 
Zone (1) embraces the central regions of Africa, Ceylon, the south 
part of the Indian Peninsula, Malaya, the Indian Archipelago, the 
northern parts of Australia, New Guinea, and other Pacific islands in 
the same latitude ; a large portion of equatorial South America, 
including Columbia, Peru, Guiana, and the northern parts of Brazil. 
Zone (2) embraces, in the New World, Bolivia, Brazil, and Paraguay 
in the Southern Hemisphere ; the West Indies, Yucatan, Guatemala, 
and part . of Mexico, in the Northern ; and Nubia, Senegambia, 
Madagascar, Mauritius, and North Australia, in the Southern Hemi- 
sphere, and South Arabia ; India, Burmah, and Southern China in 
the Northern Hemisphere. Zone (3) embraces South Africa and 
Australia, Paraguay, La Plata, and Chili, in the Southern Hemisphere ; 
and North Africa, Egypt, SjTia, North Arabia, Persia, Northern 
India, part of China, the Southern States of North America, Mexico^ 
and California, in the Northern Hemisphere. Zone (4) comprises the 
south of North America, in the New World ; the southern part of 
Europe, Asia Minor, the north of China, and Japan, in the Old 
World. Zone (5) embraces owe own country, the north of France, 
and Germany, in the Northern Hemisphere ; Tierra-del-Fuego, Falk- 
land Islands, and Kerguelen's Land, in the Southern Hemisphere. 
Zone (6) embraces the northern parts of Siberia, Norway, the Faroe 
Island^, and Iceland. Zone (7) includes the arctic regions, as far as 
inhabited ; potatoes, turnips, carrots, cabbage, &c., even growing as 
far as 71° N. There is no equivalent zone in the Southern Hemi- 
sphere. Zone (8) embraces the polar regions, where it has been 
remarked that there are more genera and fewer species. 

119. In a similar manner, in ascending from the level of the 
sea, we have at different heights distinct changes of vegetation. 
This ascent (hypsometrical) is also marked by similar belts. Thus, 
near the equator, in ascending a lofty moimtain, we may pass 
the same zones of flora as in travelling to the poles. For instance, 
at the bottom of the Alps there are vineyards in the warm climate ; 
as we ascend higher up we pass through a succession of oaks, sweet 
chestnuts, and beeches, until we reach the elevation of the stunted 
pines, &c. Thus at the height of 2,000 feet the vine disappears ; 
at 3,000 feet the sweet chestnuts cease to thrive ; at 4,000 feet the 
oak follows the same example ; at 4,700 feet the birch retires ; and 
the fir at a height of 5,960 feet, after which no tree appears. The 
rhododendron reaches to the height of 7,800 feet, and the herbaceous 
I 



130 PHYSIOGRAPHY. 

\7ill0w to about 8,150 feet ; after whicli we come to the lichena 
and mosses, which still struggle up to the snow regions. Again, 
around the base of a mountain in the torrid zone the region of 
palms extends to between 3,000 and 4,000 feet. Above this region 
extends another zone of about 1,000 feet, which is the zone of Jigs 
and tree-ferns, the next 2,000 feet including the region of the vine, 
above which appear the ordinary trees, to the height of 10,000 feet , 
and from this height to 11,500 feet we have the region of pines; 
and for the next 2,000 feet the region of the rhododendrons ; and 
for the 1,500 to 2,000 feet following appear the mosses and lichens. 
It would far exceed the limits of this elementary work to give all 
these hypsometrical zones, as they are termed, but the above will 
serve as examples. 

Not only has the climate great influence on the flora of a country, 
but also the soil, some prospering in one kind and some in another ; 
and lastly, the amount of moisture afi'ects the distribution directly 
and perceptibly. For instance, in South America, nothing seems to 
thrive until the rainy season sets in. 

Marine Vegetation. — As on land, so in water, plants have their 
fixed and natural distribution, both horizontally and vertically, 
though not so marked, owing to the greater uniformity of tem- 
pwature. 

120. Of the Four Quarters of the Globe America excels 

every other in the variety of its flora, and in luxuriance and splendour. 
It is to this country that we are indebted for the potato, maize, 
cocoa, tobacco, &c. ; while they in their turn are indebted to other 
countries for corn, sugarcane, cofiee plant, cotton plant, &c. 
Australia possesses scarcely an edible plant indigenous to it. The 
fruits now there have nearly all been introduced from Europe, 
including the vine, fig, orange, peach, &c., which flourish in the 
greatest luxuriance. Its own native trees are all evergreens, and 
chiefly gum trees, having more than a hundred species. It also 
possesses many plants which occur only there. 

Limits of Important Plants. — In the Northern Hemisphere the 
limit of trees is roughly taken to be the isotheral line of 50° (see | 
map), but in the Southern they grow all over the land, with the 
exception of the antarctic regions. The northern hmit of the culti- 
vation of grain is nearly that of the isotheral of 55°. Barley ranges 
from the isotheral of 55° to 70° ; rye from 58° to 70° ; oats from 58° 
to 72° ; wheat 59° to 75° (cannot grow in north of Scotland) ; maize 
65° to 80° ; rice 80°. The vine ranges in the Northern Hemisphere 
to about 51° N. latitude in the Old World, and only about 40" 
in the New, its limit in the Southern Hemisphere being the same in 
each, namely about 40° S. latitude. 



PHYSIOGRAPHY. 131 

LIST OF A fEW OF THE CHIEF VEGETABLE PRODUCTS AND THE CHIEF 
COUITTREES OP THEIB PRODUCTION.* 

Almond, France, Spain, Italy, Levant, Barbary. 

Aloes, Bombay, Arabia, Cape Colony, "West Indies, north of Caj^e 
of Good Hope, and Socotra. 

Arrowroot, East and West Indies, Bermudas, South America, 
Africa, India. 

Banana, all tropical and sub-tropical countries. 

Batata, all tropical and sub-tropical countries, Malayan Archipelago 

Breadfruit, South Sea Islands, and Hast Indies. 

Cacao (Cocoa), all tropical and sub-tropical countries, West India 
Isles, Caraccas, &c. 

Camphor, China, Japan, Java, Cochin- China, Borneo, and Sumatra. 

Chicory, England, Germany, and Belgium. 

Cinnamon, Ceylon and West Indies. 

Coffee, Arabia, South and Central America, Abyssinia. 

Cotton, United States, West Indies, Brazil, Egypt, East Indies. 

Currants, Greece, including the Ionian Isles. 

Figs, all tropical and sub-tropical countries, especially around the 
Mediterranean. 

Flax, Eussia, Prussia, Pei'sia, Ireland, and the tem][^ orate parts 
of Asia and North America. 

Ginger, West and East Indies, and Sierra Leone. 

Indigo, India, West Indies, Mexico, Brazil, Egypt. 

Lemon, Portugal, countries on the Mediterranean, India and Brazil, 

Logwood, Central America, West Indies, and Mexico, 

Mahogany, West Indies, South America. 

Manioc, West Indies and Africa. 

Nutmeg, East and West Indies, Brazil. 

Olive, Syria, and other Asiatic countries, and south of France. 

Opium, Asiatic Turkey, Egypt, India, and Persia. 

Oranges, Spain, Portugal, Malta, Sicily, Azores. 

Pepper, India, Further India, Eastern Archipelago. 

Pineapple, West Indies. 

Potato, Europe and America. 

Eaisins, Asiatic Turkey, and Spain. 

Rhubarb (Drug), Thibet, Chinese Tartary. 

Rice, Southern States of North America, south-east of Asia, Japan, 
India, China, Egypt. 

Rosewood, South America. 

Sago, Ceylon, India, Borneo, Singapore. 

Sugarcane East and West Indies, Brazil, India, Mauritius, 
Demerara. 

* The names printed in italics are the names of the countries of which tho 
plants are native. 



132 PHYSIOGRAPHY. 

Sugar Maple, United States, British North America, Canada. 
Tea, Cfhinttf Assam. 
Teak, East Indies, Africa, and India. 
Tobacco, United States, Germany. 

"Walnut, North America, the Himalayas, and south of Europe. 
"Wheat, United States, Russia, Germany, British North America^ 
France. 

"Wines, Spain, Portugal, France, Hvmgary, Germany, &c. 
Yam, East and West Indies, Ceylon. 

121 Animals : Their Geographical Distribution.— It has 

been estimated that the total number of known species of animals, 
including insects, is 250,000, or about 50,000 i£ we take away the 
host of protozoans (which are mostly microscopic) and insects. Out 
of this number the veHebrates — ^that is the mammals, birds, reptUes, 
and fishes — equal very nearly 20,000. This is the only division 
which needs our attention now. 

Like plants, animals have their particular zones, being influenced 
by climate and food, which also depend upon the climate; but, 
owing to their power of locomotion and dispersion, their Hmits are 
not so easily fixed, and are less precise than those of plants. StilJ 
there exists a similar horizontal and vertical arrangement of animal 
forms. The fauna of the tropics is more exuberant in numbers, 
size, strength, and beauty than that of the temperate zone, which 
in its turn excels the arctic and antarctic regions, with the excep- 
tion of marine animals and sea fowl, which are abundant in the 
latter regions. Arms of the sea and mountain chains also often 
separate the fauna of one part of a country from the other. 

The world has been divided into seven zones or regions, according 
to the character of the animal hfe. They are — 

(1) Pal^ ARCTIC Region, including Europe, Timis and Algeria, 
Northern Asia, Northern China, part of Mongoha, Japan, the deserts 
of Central Asia, Persia, Asia Minor, and Japan. The chief animals of 
this division are — Mammals : Bear, fox, wolf, badger, glutton, sable, 
lynx, monkey of Gibraltar, squirrel, hare, rabbit, rat, mouse, beaver, 
lemming, horse, ass-, wild boar, stag, musk-deer, goat, reindeer, 
chamois, auroch, moufflon, hedgehog, mole, shrew, and bat. Bibds ; 
"Vulture, buzzard, osprey, eagle, owl, falcon, kite, thrush, finch, wax- 
wing, crossbill, bee-eater, oriole, woodpecker, cuckoo, pigeon, par- 
tridge, grouse, quail, francolin, goose, swan, duck, gull, pelican, 
diver, puf&n, flamingo, grebe, snipe, crane, bittern, stilt, spoonbill, 
and coot. This is the richest region of birds, Europe containing no 
less than 600 species. Reptiles : Frog, toad, newt, tree-frog, triton, 
proteus, common snake, viper, chameleon, lizard, gecko, turtle, and 
tortoise. 

(2) Ethiopian Region, -embracing the west, south-west, south- 
east, and north-east of Africa, Arabia, Madagascar, and the Masca« 



PHYSIOGRAPHY. 133 

rene Islands. Mammals : Bear, lion, leopard, jackal, fox, wolf, 
hyena, ratal, cheetah, squirrel, porcupine, hare, rat, mouse, baboon, 
gorilla, chimpanzee, lemur, antelope, gazelle, giraffe, Arabian camel, 
zebra, eland, gnu, ibex, addax, rhinoceros, boar, hippopotamus, 
and elephant. Birds: Vulture, eagle, falcon, owl, hoopoe, wax- 
wing, colic, hornbill, oriole, parrot, cuckoo, honey guide, pigeon, 
guinea fowl, quail, ostrich, crane, bittern, ibis, snipe, adjutant, 
albatross, and pelican. Keptiles: Crocodile, lizard, gecko, land 
tortoise, frog, lepidotis, coccUia, and cobra. 

(3) Indian Eegion, which embraces British India, Central and 
Southern China, Burmah, Siam, Cochin, Malaysia, the IsTicobar and 
Andaman Islands, East Indies, and the Philippine Islands 
Mammals : Monkey, ourang-outang, flying lemur, fox, bat, shrew, 
banxring, bear, lion, jackal, wolf, leopard, tiger, cheetah, squirrel, 
hare, rat, mouse, antelope, bufialo, yax, zebu, sheep, goat, gazelle, 
ibex, hog, wild boar, rhinoceros, elephant, tapir, phalanger. Birds : 
Eagle, vulture, osprey, kite, owl, falcon, hornbill, colic, bee-eater, 
hoopoe, sunbird, waxwing, bird of paradise, edible swallow, tailor 
bird, paroquet, woodpecker, cuckoo, lory, honey-guide, channel-bill, 
peacock, pheasant, francolin, mound bird, crane, bittern, snipe, 
adjutant, pelican, flamingo. Reptiles : Chameleon, dragon lizard, 
gecko, sea-snake, cobra, frog, cocciHa. 

(4) Ne arctic Region, including Gfreenland and North America, 
as far down as Mexico. Mammals : Puma, civet, wolf, bear, sea- 
otter, sable, lynx, dog, squirrel, hare, beaver, porcupine, rat, mouse, 
musk-ox, elk, bison, sheep, bighorn, prongbuck. Birds : Eagle, 
vulture, osprey, falcon, owl, turkey, thrush, humming-bird, mocking- 
bird, finch, waxwing, cedar-bird, crossbill, Carolina paroquet, cuckoo, 
raven, crow, pie, jay, woodpecker, quaU, grouse, flamingo, goose, 
duck, albatross, diver, puffin, tern, grebe, pigeon. Reptiles : AlUgator, 
tortoise, lizard, snapping turtle, rattlesnake, tropidonotis, bull-frog, 
triton, siren, proteus. 

(5) Neotropical Region, including Central America from Mexico 
to Panama, the Andes to Bolivia, the highlands in the basins of the 
Amazon and Orinoco, Guiana, S.E. of Brazil, Paraguay, ChUi, 
La Plata, Patagonia, the West India Islands or Antilles. Mammals : 
Bear, puma, jaguar, racoon, coati, kinkajou, squirrel, hare, porcupine, 
cavies, chinchilla, agouti, rat, mouse, monkey (including those with 
prehensile tails, as marmosets and sajous), bat, vampire, ant-bear, 
ant-eater, armadillo, llama, alpaca, guaruti, guanaco, vicuana, tapir, 
peccary, opossum, yapock. Birds : Condor, vulture, kite, owl, 
caracara, humming-bird, umbrella-bird, trogon, bell-bird, plant- 
cutter, boat-tail, creeper, cuckoo, cockatoo, parrot, toucan, macaw, 
avis, turkey, quail, curassow, spoonbill, ibis, trumpeter, adjutant, 
flamingo, penguin, grebe, petrel, tropic bird. In this region it may 
be mentioned that upwards of 400 species of humming-birds are tc 



134 PHTSIOGRAPHT. 

be found, and ot the splendid tanagers 193 out of the 222 known 
species belong to South America. Eeptiles : Alligator, lizard, boa, 
rattlesnake, turtle, lepidotis, coccilia, tree-frog, toad, and iguano. 

(6) Australian Eegion consists of Australia and the eastern half of 
the Malayan Archipelago up to Wallace's line. The chief animals of 
this region are the pouch-bearers. There are neither monkeys, 
cud-chewers, or thick-skinned animals. Mammals : Kangaroo, 
wombat, phalanger, koala, pouched-woK, dasyurus, banded ant-eater, 
echidna, and ornithorhynchus (a mole-shaped animal, with a jaw like 
a duck's bill). Birds : Parrots, cockatoos, and grass-paroquets are 
numerous ; the cuckoo, woodpecker, bower bird, thrush, lyre bird, 
oriole, honey-eater, emu, falcon, black swan, and goose. Reptiles : 
Snakes, landosca, Hzards, moloch, tortoise, and gavial. 

(7) Pacific Region, New Zealand, Polynesia, &c. Very few 
animalsinhabit this zone, the only ones being bats. Birds are plentiful, 
and include parrots, paroquets, honey-eaters, finches, plumed birds, 
the apteryx of New Zealand (wingless), lory, tropic bird, and coot. 
Reptiles : Turtle, iguana, lizard, sea-snake, &c. This latter region 
is sometimes joined to the Austrahan. 

Animals Peculiar to Certain Regions. — Each quarter of the globe 
has its own class of animals preponderating. Europe and Asia 
have the ruminantia ; Africa, land tortoises ; North America, birds of 
passage ; South America, the edenta, or toothless animals ; Australia, 
marsupialia, or pouched animals. In many cases they are 
confined to their own country. For instance, the reindeer and 
hamster are confined to the very north of Europe ; the chamois 
and ibex, the Alps ; the aurochs, the Caucasus and crown forests of 
Russia ; the marmot, the Alps and Pyrenees ; the kangaroo and 
ornithorynchus, to Australia, in which country the three great 
orders of animals are entirely wanting — namely, the ruminantia^ or 
those that chew their cud, as the ox, sheep, &c. ; the pachydermata, 
thick-skinned animals, like the horse, elephant, &c. ; and the 
quadrumana, or four-handed animals, such as monkeys, apes, &c. 
The hippopotamus and giraffe are confined to Africa ; the camel to 
the dry deserts of Africa and Asia ; the tsetse (an insect whose bite is 
death to certain animals) is often confined to the regions lying on one 
side of a river, in different parts of South Africa ; the hyena, quagga, 
and Cape bufiialo to South Africa i The true humming-birds, some 
of which do not weigh more than 20 grains when ahve, entirely 
belong to South America, also the llama, alpaca, ocelot, prehensile- 
tailed monkey, the condor, the rhea, and the hang-nests. The 
cashmere goat, musk-deer, panui sheep, are common to Central Asia ; 
the royal tiger, to Southern Asia. Among the marine animals, the 
right whale, seal, and walrus, are confined to the Arctic Sea ; the 
sperm whale is never found out of the tropical parts of the Pacific. 
The coral insects only exist in tropical and sub-tropical regions ; and 



PHYSIOGRAPHY. i 135 

the herring, cod, salmon, &c., only reach perfection in the colder 
seas. 

122. Representative Species. — ^Some animals of the Old 

World, though not appearing in the New, may be said, roughly, to 
be represented by species in many points similar. Thus, the camel 
of the Old World is represented by the llama and alpaca of the 
New, their habitat being nearly the same as the camel ; the lion 
and tiger of the Old are represented by the puma and jaguar of the 
New ; the ostrich of Africa by the rhea of South America and 
the emu of Australia ; the crocodile of the NUe by the gavial of 
the Ganges and the alligator or cayman of the Amazon and Orinoco. 

123. Distribution of Marine Life.— Professor E. Forbes 
sketched a scheme of Bathy metrical distribution — ^that is, distribu- 
tion in depth, arranging the ocean into four zones. (1) The 
Littoral Zone, lying between high and low water marks, and 
characterised in our own seas by such shellfish as periwinkle, mussel, 
cockle, limpet, razor-shell, &c. (2) The Laminarian Zone, extending 
from low- water mark to the depth of 15 fathoms, and including such 
fish as the starfish, sea-urchin, tubularia, modiola, and pullastra. 
(3) The Coralline Zone, in which the corals, &c., are the typical 
inhabitants, extending from 15 to 50 fathoms, and characterised by 
the disappearance of ordinary sea shells, but abounding in buccinum, 
fusus, venus, pecten, &c. (4) The Deep Sea Coral Zone, extending 
to 100 fathoms and more ; containing brachiopod mollusca that 
cannot exist in shallower waters, cidares, &c. 

That marine animals can exist at great depths of the ocean is fully 
proved by the Challenger expedition of 1873-76, which, during its 
explorations and dredging operations, brought up multitudes of 
living creatures (many of which were unknown before) from the 
depth of three miles and more. 

horizontal Distribution. — The fishes and shellfish of the tropics 
are noted for then- varied and brilliant tints ; while those of the 
Arctic Seas are of uniform and sombre hues. The right whale is 
not found beyond the cold waters of the higher regions in either 
hemisphere, the sperm whale keeping to the tropical areas of 
the Pacific. The seal and walrus also keep to the colder, temperate, 
and arctic regions. The cod, herring, haddock, salmon, &c., thrive 
best in the colder waters of the higher latitudes. The shark prefers 
the waters of the torrid zone, and the coral builders only exist 
within the tropical and sub-tropical regions. 

DISTRIBUTION OF MAN. 
124. Man is more capable of adapting himself to any 

climate than any other animal, being able to live under extreme 
degrees of heat and cold, and on a greater variety of food. The 



136 PHYSIOGRAPHY. 

next to man in both these respects is the dog, his faithful companion 
and friend. Though man can adapt himself to different climates, 
yet he is, in common with the other animals, influenced by external 
circumstances, but in a less degree. 

Though there are what are termed different races of men, yet 
there is but one species, the different races being only different 
varieties, the diversities having arisen from the long-continued action 
of climate and other external influences. In a similar manner the 
difference in species or varieties of other animals that have in suc- 
cession inhabited this globe may be considered as the 7'esuU of the 
gradual modification of pre-existing species; and so also with the 
plant life of the globe. This is what is termed the doctrine of 
evolution. 

125. Classification of Races. — There has been several dif- 
ferent classifications put forth, one of which until lately obtained 
great currency, viz., Blumenbach's, which divided them into five 
divisions: (1) the Caucasian, (2) Mongolian, (3) African, (4) Ameri- 
can, (5) Malay ; but the most modern classification is into three 
primary races — the Caucasian, or white and bearded race ; the Mon- 
gohan, or tawny and beardless race ; and the Negro, or black-skinned 
and woolly-haired race. 

Caucasian, or White Race, with straight oval face, large broad 
forehead and skull, narrow nose, small mouth, thin lips, large eyes, 
tall in stature, and very intellectual. They occupy nearly all 
Europe, South- Western Asia, Northern Africa, and extend from 
Iceland to the Ganges, and from the Tropic of Capricorn to the Arctic 
Circle. 

Mongolian Race. — Head nearly round, but narrow at the top, and 
low forehead ; broad flat cheek bones, which are also prominent ; 
yellow skin, stature short, eyes obliquely set, and next in intellect 
to the above race. This class includes all the rest of Asia and 
Europe not included in the Caucasian. 

The Negro, or Ethiopian Race. — Narrow head, elongated back- 
wards ; narrow convex forehead, low and retreating ; nose broad and 
flat, projecting jaws, upper teeth turned obliquely forward, thick 
lips, crisp and woolly hair, and skin black. They occupy the whole 
of Continental Africa, south of the Tropic of Cancer. The true 
Negro is confined to the district between the Desert of Sahara and 
northernmost border tribes of the Hottentots and Kaffirs in South 
Africa. 

In addition to the above there are several minor varieties, which 
may be regarded as modifications and an intermixture of the three 
primary races. They are the Malays, in Malaysia and Madagascar; 
the Papuans, in New Guinea, New Hebrides, &c, ; the Maoris of 
Australia and New Zealand ; and the Amencan or Red Indians, the 
aborigines of North and South America. These may be regarded 
as Mongolians. 



PHYSIOGRAPHY. 137 

126. Huxley's Classification.— Professor Huxley divides them 
into two varieties, according to the character of the hair. (1) The 
Ulotrichi, having crisp or woolly hair. (2) The £eiotrichi, having 
smooth hair. The first race (1) varies in colour from yellow and brown 
to the darkest colour of human skins, termed black, and they are 
dolichocephalic ; "* that is, their skulls are longer than broad. This 
class includes the Negroes, Bushmen, and Malays. Class (2), the 
Leiotrichi, is divided into four divisions — viz., the (a) Australoid 
Group, with dark skin and eyes, long wavy black hair, dolichocephalia 
skulls, with well-developed brow ridges, broad nose, and heavy 
projecting jaws. This group includes the natives of Australia 
and the coolies. (6) The Mongoloid Group, with yellowish or 
reddish brown skins, black eyes and hair. It includes the Chinese, 
Japanese, Tartars, Polynesians, Esquimaux, and American Indians, 
(c) The Xanthocroic Group, of fair, white, clear skin, grey or blue 
eyes, includes the Slavonians, Teutons, Scandinavians, and fair 
Celtic speaking nations, {d) The Melanochroi, or dark whites, 
with pale complexions, dark eyes and hair, includes the Iberians, 
black Celts of Western Europe, dark-complexioned whites of the 
Mediterranean, Western Asia, and Persia. This group is probably 
a mixture of Australoids and Xanthochroi. 

Man's influence on the life of animals may be noticed in two ways 
especially. (1) In preservation^ as in the case of the horse, ox, dog, and 
other animals, which man domesticates as well as preserves, making 
them useful companions. (2) Extermination. Such animals as are 
dangerous to man, or destructive to his property, are speedily 
exterminated, or driven out to less frequented spots ; as, for 
instance, the wolves and bears of England, which have been long 
exterminated — other animals are also exterminated by the great 
demand for their skins — others in the chase. The influence of man 
may also be noticed in transferring animals from their own region 
to another ; as, for instance, the domestic animals — horse, sheep, 
dog, &c. — have been taken by man into nearly all the habitable 
regions of the globe. The horse has probably been brought from 
Asia to our own country ; but the dog is the only animal that can 
adapt itself to aU climates, like man. Many animals, as the camel, 
reindeer, &c., cease to exist away from their own particular 
habitat. 

The Population of the Glole. — According to the latest authorities 
the population of the difierent continents is as follows : Europe, 
309,178,300; Asia, 824,548,500; America, 85.519,800; Africa, 
199,921,600 ; and Oceanica, 20,000,000 (of which Australia has 
5,000,000) ; making a total of 1,439,168,200 persons. 

* Skulls are called dolichocephalic when the breadth is less than four-flftha 
of the length, and brachycephalic, when more than four-fifths. 



APPENDIX. 



(n the former pan of this work will be found all that is necessary 
tor the elementary stage, and also part of the advanced. In this 
appendix is given the extra matter required for the advanced 
stage. 



LIGHT AND HEAT FROM THE SUN. 

Regarding the nature of the light and heat transmitted to us from 
the • sun two theories have been advanced, namely, the emission 
theory and the undulatory theory. The former, which is generally 
attributed to Sir Isaac Newton, supposes light to consist of infinitely 
small lumiuiferous particles of matter, emitted with exceeding 
celerity, capable of producing light and heat when they strike 
against bodies. This theory has given way to the latter, or undu- 
latory theory, which assumes that there exists ever in space, and 
between the particles or molecules of all matter, an exceedingly 
rarefied, highly elastic substance, termed ether, which is 39,000,000 
times thinner and 1,278 times more elastic than air, and that it is 
to the undulations and vibrations of this substance that we owe the 
phenomena of light and heat, the light being produced by the 
action of luminous bodies upon the ether, and the heat by the vibra- 
tions of the particles of a body, each particle being supposed to have 
a motion either backwards or forwards, but so rapid that the eye is 
unable to perceive it. The more rapid the motion the greater the 
heat. This ether, when excited by the presence of hot and luminous 
bodies into undulations, produces impressions of light and heat on 
bodies that encounter the waves. 



127. Solar Radiation.— Effects on the Vegetable 

Kingdom. — That solar radiation has great influence on the 
vegetable kingdom is at once evident from the variation and 
difierences between the difierent zones of climate. Thus, 
in every zone we find the vegetable organization peculiarly 



APPENDIX. 139 

fitted for th.e consideration by which, it is surrounded. At the 
equator we have the nutmeg, clove, cinnamon, pepper (spices) ; the 
sandal, ebony, banyan, and teak ; frankincense, myrrh, and many other 
iwccwse-bearing plants ; the coffee and tea plants, &c. In Spain, Sicily, 
and Italy, we have the orange and lemon trees. As we travel 
further north the weakness of the solar radiation becomes greater, 
causing differences in the zones. (See "Distribution of Vegetation.") 
These differences all depend on the solar radiation. From photo- 
graphic phenomena we have evidence that the constitution of the 
solar rays varies with the latitude, hence the cause of the changes in 
vegetation. The effects of the sun's rays in France and England, in 
producing chemical changes, are infinitely more decided than, with 
far greater splendour of light, they are found to be in the lands 
under or near the equator. 

Again, it is the actinism, or chemical power, of the sun's rays that 
excites germination in plants. It proceeds from the blue ray of the 
spectrum, and is the same power which acts on the sensitive paper 
of the photographer. The luminous power of the yellow ray excites 
the formation of leaf and wood ; that of the red ray the development 
of flower and fruit. 

It is also a well-known fact that many creepers will twine in the 
sunHght, but when put in total darkness they will grow perfectly 
straight. Exceptions are the liean and the ipomoea purpurea, which 
continue to twine round their supports in the dark. 

128. Propagation of Light. — Light, as previously stated, is the 
result of wave-motion, the waves being of extreme minuteness and 
propagated in straight lines at the rate of 186,000 miles per second, 
the vibrations of the ether taking place at right angles to the 
direction of propagation. 

Kegarding the rays of light, though they proceed in straight lines, 
yet on proceeding out of a rarer into a denser medium they are bent 
or refracted out of their course, a familiar example of which is 
noticed in the case of a stick, partially immersed in a basin of water, 
appearing broken at the surface of the water, and the part below 
seem i ng higher than it really is. A similar occurrence takes place 
when the sun's rays enter the atmosphere of this earth, some being 
reflected back, while the remainder are refracted downwards towards 
the earth (see "Atmosphere — Twilight"); but the further they 
advance through the atmosphere the more they are bent, owing to 
the density of the air continually increasing, so that the rays when 
they have arrived at the earth's surface have travelled through a 
parabohc curve. The tangent to this curve at the surface of the 
earth is the direction in which the celestial object appears, causing 
the sun and other heavenly bodies to appear higher in the heavens 
than they really are. The law of refraction is that for the sarm 



140 APPENDS. 

media the sine of the angle of incidence is always proportional to the 
sine of the angle of refraction. Hence, in calculating the angles 
taken in measuring the distances and size of the sun and other 
heavenly bodies, notice must be taken of refraction. Thus, when 
the apparent zenith distances have been observed with the mural 
circle, they must be corrected by the addition of the refraction. 

PARALLAX. 
129. How to find the distance of the heavenly bodies.— 

It is from the parallax, or the apparent change of position in an 
object arising from a real change of position of the observer, that 
the distances and magnitudes of planets are calculated. These are 
measured by the angle formed at the object by two straight lines 
-jlrawn from it to the two positions of the observer, but as the 
distance of any planet from the earth is extremely great we may 
assume without any sensible error that lines drawn from anyone of 
them to the earth's centre, and any point on its surface, are 
absolutely coincident when the body is in the horizon. The angle 
made by these two lines is called the horizontal parallax. 

In taking the horizontal parallax the two stations of the observers 
should be as far apart as regards latitude as possible, and also be 
situated nearly on the same meridian. Having these properties are 
the stations at Greenwich, N. lat. 51° 28' 38", and the Cape of Good 
Hope, S. lat. 33° 56', E. long. Ih. 13m. 55s. To find the distance of 
the moon, take this as th« base line of a triangle, and from the angle 
made by lines drawn from the moon to these places, the sides of 
the triangle can be determined, in proportion to the earth's radius. 
Tjie parallax is greatest when the object to be measured is on the 
horizon. The mean parallax of the moon is 57' 2"5," which corres- 
ponds to an average distance of 6O5 times the earth's radius, or 
238,851 miles. Thus, when the parallax is obtained we have the 
three angles of a right-angled triangle, and one side to fiud the other 
sides. By trigonometry let A represent the parallax, and a the 
given side, or radius of the earth, C the right angle, and B the 
remaining angle ; then B=:90°-A, and calling the remaining sides 
6 and c respectively, c being the hypothenuse, and proceeding from 

the centre of the earth. Now, - = tan. B, orlog. & = log. tan. B-10 
a 

+ log. a ; and - = sin. A, or log. a -log, c=log. sin. A- 10; orlog. c 

c 
= 10 + log. a -log. sin. A. Hence, substituting data, A=£7'2'5"; 
a = earth's equatorial radius = l; log, c=10 + log. 1 - log. sin. 
57' 2-5"= 10- 8-2204661 =log. 1-7795339 = log. of 60-249 = number of 
times earth's equatorial radius (say 6O5), which gives the distance 
as 3962-8 x 60-25 = 238,858 miles. 



APPENDIX. 141 

Generally, in the case of planets, the parallax is too small to be 
measured Meetly, so that other circumstances have to he taken 
advantage of. Thus the transit of Veniis over the sun's disc on 
December 9th, 1874, was taken advantage of, with the view of 
obtaining the correct parallax of the sun, which is now given as 
8'879",* giving a httle over 92 million of miles as the distance of the 
sun from the earth. Another transit occurs in 1882, when this 
question will in all probability be settled. The periods between the 
transits are 8 and 125J years alternately. 

The parallax of the chief planets is as follows : Mercury 16", Venus 
32", Mars 24", Ceres 5", Jupiter 2", Saturn 1", Moon 57' 27", &c. The 
diameter of these planets may be measured by means of micrometers, 
and found to be as follows : The Sun 1923-7", Mercury 11", Venus 57", 
Mars 26-8", Jupiter 41", Saturn 18", Moon 1920". So that we can 
compare the real diameters of these bodies with the diameter of the 
earth. For diameter of planet : diameter of the earth :: angle 
planet subtends at the earth : angle earth subtends from planet. 
Thus, taking the sun, for instance, we have the proportion 
x: 1 .: 1923-6 : (8*879 x 2) ; or, diameter of sun = 1923*6' -^ 17-758 
= 108 times the diameter of the earth = 855964 miles, nearly .+ In 
a similar manner we find the diameter of the other planets to be — 
Mercury 2961 miles, Venus 7511, Mars 4921, Jupiter 88390, 
Saturn 71904, Moon 2159.+ 

The day or time of revolution of each planet is as follows : — 

Dys. Hrs. Min. Day Hrs. Min. 



The Sun 25 7 48 

Mercury 10 5 

Venus 23 21 



Mars 1 37 

Jupiter 9 65 

Saturn 10 29 



Uranus, 9hrs. 30min. 

The table given on the following page gives the distances, dimen- 
sions, weight, &c., of the planets. It is on the accuracy of the Sun's 
distance from the earth that our knowledge of the sizes, distances, 
weight, &c., of the planets, and also of the sun, depends. Hence the 
importance of this problem, which will account for the hundreds of 
years that have been spent (records of which we have from about 
400 years B.C.) in attempting to solve this question. 

* When we know the angle the earth's disc subtends from a planet its 
distance can approximately be found by dividing 206,265 (the seconds in arc 
equatorial radius) by the number of seconds in the angle. Thus in the case 
of the sxm the angle = 8-879 x 2 = 17-758", therefore distance roughly = 

^^S = 11609 diameter of the earth = 7925*6 X 11609 = 92,008290 mUes. 

t The diameter of the s\m given in the table is obtained by taking the 
parallax as 8-943" instead of 8-879", as used here. 

t The contents in cubic miles = cube of the diameter multiplied by -5236, 
and their mass, compared to the earth's, equals the cubic contents multiplied 
hv the specific gravity 



142 



APPENDIX. 



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APPENDIX. 143 

THE PLANETS. 
130. The Atmosphere, Temperature, &c.— Not mucli is 

known of Mercury, the planet nearest the sun, but it is believed to 
possess a dense cloudy atmosphere, which possibly may protect it 
from the great heat of the sun ; but, supposing all our heat to come 
from the sun, it is calculated that the mean heat in Mercury is above 
the boiling point of quicksilver, and even near the poles water would 
always boil. Mountains have been seen on its surface ten miles 
high. The orbit of Mercury makes an angle of 7° with the ecliptic. 
The next planet (omitting Vulcan, of which very little indeed is 
known) in nearness to the sun is Venus, the morning and evening 
Btar, for when to the west of the sun it rises before it, being 
then called the " morning star ; " but when it is to the east of 
the sun it sets after twilight, being then termed the "evening 
star." The orbit of this planet makes an angle of 3J° with the 
ecliptic, and the inclination of its equator to the plane of orbit is 
49° 58'. That this planet possesses an atmosphere of considerable 
density is now certain, its horizontal refraction having been found very 
nearly equal to that of the earth by observing the amount of twilight 
upon the illuminated portion of the planet. According to Vogel 
the atmosphere contains aqueous vapour. The temperature of Venus, 
though probably mitigated by her atmosphere, must be far too 
high for the existence of either animals or plants ; and also the 
inclination of her axis, which is affirmed to be more than 60°, would 
cause very great changes in the seasons. The next planet from the 
sun is the Earth (see page 63) ; after which comes Mars, the most 
remarkable of all the other planets — as it appears to be the only one 
with any probability of being inhabited excepting our earth. It 
also resembles our earth in one or two circumstances — namely, in its 
revolution, which takes very nearly the same time as our earth, 
24h. 37m. The inclination of its axis to the ecHptic is also nearly 
the same as the earth — about 28° 51' — and its orbit makes an 
angle with the ecliptic of 2°. Its surface also appears to consist of 
land and water — about five times as much land as water. Around the 
poles its surface is white, which increases in size as the winter 
appears in that hemisphere, and less in surmner. Hence we concLide 
that it has polar snows similar to our earth. It is considered certain 
that this planet is enveloped in an atmosphere of considerable 
density, and its temperature, owing to its greater distance from the 
sun, must be colder than that of our globe, which will account for the 
continual snow seen on its surface. The land on its surface appears 
of a reddish tint, and gives rise to the fiery appearance of the planet 
to the naked eye. It is supposed that this is the real colour of the 
soil ; so that its crust is something like the red sandstone of oiir 
globe. The waters appear of a bluish-grey colour. It has lately 
been discovered that this planet possesses two satellites. 



144 APPENDIX. 

The next planet, passing over the asteroids, is Jupiter, the largest 
of the solar system. Its disc is usually crossed by dark-coloured 
belts or cloud belts, parallel to its equator. This planet is surrounded 
by a dense cloudy atmosphere, which is capable of reflecting the 
solar light. The dark belts are, probably, openings in the clouds, 
through which we see the darker surface of the planet ; or, more 
probably, lower beds of clouds beneath. These belts contiauaUy 
change in number and size, and are supposed to be caused by 
violent permanent winds. There are also to be seen occasionally 
small bright spots resembling patches of floating cloud, which have 
been supposed to be masses of cloud floating round about the 
summits of high mountains. Jupiter's time of revolution or day, 
as determined by these spots, is 9h, 55m. 50s. Its orbit makes an 
angle of 1^° with the ecliptic, and the inclination of its equator to 
the plane of orbit is 3° 4'. It is attended by four satellites or moons, 
revolving round him from west to east, similar to ours. (See 
" Satelhtes.") 

The next planet is Saturn, which has a most remarkable 
appendage — namely, a luminous ring, or rings, by which he is 
generally seen to be surrounded. The general appearance of these 
rings is that of three, lying outside of each other in succession, the 
two outer ones being the brightest, and the inner one appearing 
transparent, and only just visible with a large telescope ; the 
diameter of the outer ring is 166,000 miles, but not above 130 to 
140 in thickness. They are supposed to consist of millions of small 
satellites revolving round the primary planet. 

Regarding these riogs Sir J. Herschel, in his valuable work, writes : 
** They must present a magnificent spectacle from the regions of the 
planet which lie above their enhghtened sides, as vast arches 
spanning the sky from horizon to horizon, and holding an almost 
invariable position among the stars. On the other hand, in the 
regions beneath the dark side a solar ecHpse of fifteen years* 
in duration, under their shadow, must afibrd (to our ideas) an 
inhospitable asylum to animated beings, ill-compensated by the faint 
light of the satellites. But we shall do wrong to judge of the fitness, 
or unfitness, of their condition from what we see around us, when, 
perhaps, the very combinations which convey to our minds only 
images of horror may be in reality theatres of the most striking 
displays of beneficent contrivances." 

Saturn appears to have an atmosphere dense and cloudy, similar 
to that of Jupiter, and is attended by eight satellites. Its orbit 
makes an angle of 2^° with the ecliptic, and the inclination of its 
diameter with the plane of orbit is 26° 49'. 

We now come to Uranus, of which very little is known ; but it is 
worthy of note that the distance of this planet is so great that 
the light and heat it can receive from the sun is only -^s part of 



APPENDIX. 145 

the intensity on tlie earth. It has also four satellites in attendance 
upon it. Angle that Uranus makes with the ecliptic is 47'. 

The most distant of all the planets is Neptune, which shines like 
a star of the eight magnitude. It has one satellite only at present 
discovered. Owing to its great distance from the sun, it will shine 
upon it with only 75-5-0- P^'i't of its intensity on the earth. Inclination 
of orbit 1° 47', and of diameter with plane of orbit 26°. 

From the above short descriptions of the planets we see that none 
of them are favoured like ours. It is situated at a medium distance 
from the sun, so that we are exempt from the extremes of heat and 
cold ; again, its orbit lies in the plane of the sun's equator, but the 
others are inclined more or less to it. The only other planet that 
appears to have the slightest possibility of being inhabited is Mars, 
and there the cold must be as severe in their summer as it is in our 
arctic and antarctic regions. Our planet is also the only interior 
one that possesses a satellite. (For distance of planets from the sun, 
their sizes, density, &c., see Table of " Solar System.") 

131. Satellites. — With the exception of the satellites of Uranus 
they all revolve round their primaries from west to east, and rotate 
on their axes in the same direction as their primaries, and also in 
exactly the same time as their times of revolution round those 
bodies. The most interesting of the satellites to us is evidently our 
own. (For description and particulars see 60.) 

The density of all the satellites has not as yet been ascertained. 
Those known are the Moon, "61, or a little over f of that of the 
earth ; Jupiter's 4 average about "288, or a little more than \ of that 
of the earth. Those of Saturn are supposed to be about "134, but 
not known for certain. 

That our moon possessed no atmosphere has long been the 
opinion. The spectra of various parts of its surface, when examined 
under various conditions of illumination, showed no indication of an 
atmosphere. 

The orbit of the moon is incHned to that of the earth at an angle 
of 5° 8'. If it were not inclined there would be an eclipse of the 
sun and moon once every fortnight. Eclipses of the sun take place 
when the moon, passing between the sun and the earth, intercepts its 
rays. Those of the moon take place when the earth, coming 
between the sun and moon, deprives the moon of its light. Hence 
an eclipse of the sun can only take place when the moon changes, 
and an eclipse of the moon only when the moon fulls, for at the sam, 
time of an eclipse, either of the sun or of the moon, the sun, earth 
and moon must he in the same straight line. A total eclipse of the sun 
occurs when the moon is near the earth, and in the same .«traigh<- 
line as the earth and the sun. An annular eclipse takes place when 
the moon is more remote from the earth, but in the same straight 
line, 

K 



146 APPENDIX. 

COMETS AND METEORS. 

132. Comets, like planets, revolve round the sun, evidently under 

the influence of the law of gravitation, but their orbits are much 
more elliptical, though always identical with one of the conic 
sections, and obeying Kepler's second law — namely, of the equal 
description of areas — as the correct predictions of their return show. 

The inclination of the orbits have all degrees of magnitude, and 
their motions in their orbit are as often retrograde as direct. 
Sometimes one approaches near to the sun, and afterwards recedes to 
a distance of many hundreds of times the distance of the earth 
from that luminary. For instance, the periodical comet of 1680, 
whose period is 575 years, approaches to within one-sixth part of the 
diameter of the sun from its surface, and when farthest away its 
distance exceeds 138 times the distance of the sun from the earth. 
It is also calculated that the period of the great comet of 1811 is 
3065 years. The orbits of the great majority differ very little if any 
from that of a parabola during the time they are visible to us. 
Hence we conclude that they will not return to the sun ; or that 
the distances to which their orbit extends is so enormous as to 
require the lapse of ages to perform their revolution. At the same 
time there are a few others which recede only a very short distance 
in comparison — as in the case of Encke's, whose orbit is within 
Jupiter's, appearing every 3;^ years ; Bicla's, appearing every 
6f years ; Faye's, 7^ years ; and Halley's, 76 g years. 

Their form generally consists of three parts — the nucleus, or 
brightest and densest part ; the coma, a nebulous haze or cloud 
eurrounding the nucleus like an atmosphere ; and the tail, a conical 
appendage, stretching often to immense distances, and mostly in 
opposite directions to the sun. Some comets appear without tails. 

Regarding their constitution not much is at present known, but it is 
found by telescopic observations, and also by the insignificant effect 
produced on the motions of planets when comets approach near 
them, that the masses of all the known comets are exceedingly 
small, even of incomparably less density than our atmosphere, or of 
any gas with which we are aquainted ; as, through even the densest 
part, the faintest stars may be seen — thoitgh a slight fog near the 
surface of the earth prevents stars of the first magnitude from 
being visible. 

133. Meteors and Meteorites. — In close connection with 

comets are meteors and meteorites — the spectrum analysis showing 
a similar identity of materials agreeing with the constituents of 
the sun and of the planets. These meteors are of various sizes, but 
are too small to be visible by reflected light. They appear as groups 
or clouds, each one. of which pursues a definite and fixed orbit, 
which are similar to the orbits of the comets — the latter being now 



.APPENDIX. 147 

considered as clouds of meteorites. On entering our atmosphere 
they are known as shooting stars, sometimes exploding in their passage 
through, owing to the rapid motion with which they strike the 
particles of air. They are then termed Jire balls. Sometimes the 
fragments of these explosions fall to the earth as meteorites or 
aerolites. 

The groups of meteors sometimes come in the track of the earth, 
so that when the earth passes through or near the track of one of 
them we have a star shower. These showers are greatest between 
August and November. The maximum brilliancy occurs every 33|: 
years, and then sometimes for four or five years in succession there 
are showers of unusual brilliancy. While on the subject of meteors 
we will just draw attention to the ideas of Mr. R. A. Proctor on this 
subject and the growth of the earth. His opinion is that the earth 
is, has always been, and so long as it shall exist as a part of our cos- 
mical system, must ever continue to be, growing in size. Meteors are 
bodies composed of extra-terrene matter, which travel in vast belts 
and in highly eccentric orbits round the sun. These systems of meteors 
or belts are very numerous, and when their orbits intersect that of 
the earth they are brought within the influence of its gravitation, and 
on entering our atmosphere become luminous and fall to the surface 
of our planet. In the periodical showers of shooting stars which 
are so well known, not a night passes in which some falling stars are 
not seen, and in certain months and on particular nights the golden 
rain is incessant. Of course, too, meteors fall in the daytime, 
though unseen. It has been calculated, says Mr. Proctor, that 
hundreds of thousands of these extra-terrene bodies become incor- 
porated with the earth every 24 hours, and four hundred milhon in 
the course of a year. These may vary in weight from a few graina 
to a ton. One is known to have fallen in South America weighing 
15 tons. Yet these small accretions to the earth's matter would take 
many millions of years to add a single foot to its diameter. 

It has been suggested that it is to these meteors, &c., that the sun 
owes its continuation of heat and light, there being an incessant 
flow of cosmical matter and aerolites towards the sun, which absorbs 
them, and is thereby enabled to continue its emission of light and 
heat. Accompanying the sun there is a hazy nebulous cone of 
light, which indicates the existence of a mass of material particles, 
supposed to be myriads of meteors revolving round the sun in spiral 
orbits and continually falling into it. 

Sir W. Thomson supposes that these have to make their way 
through a resisting medium of increasing density as it approaches 
the sun. Thus the friction arising from the rapid motion of each 
particle through this medium will render the particle itself incan- 
descent, and the heat thus generated will contribute to the sun'a 
heat. 



148 APPENDIX. 

FIXED STARS. 
134. Number, Distance, and Magnitude of the Stars.— 

The stars which are popularly called fixed, on account of their 
appearing to preserve year after year the same relative position in 
the heavens, are really not so, as the greater part, if not all, have 
measurable motions of their own. 

The stars being at such enormous distances from us are dis- 
tinguished only by their different degrees of brightness or magni- 
tude, as it is generally termed, and from this difference they have 
been separated into classes, the brightest being said to be of the 
first magnitude, the next of the second magnitude, and so on to 
the sixteenth magnitude, which requires the m/)st 'powerful telescope 
to view them. Those visible to the naked eye are included in the 
first six classes, and number nearly 5,000 near the equator. Very 
seldom more than 3,000 can be seen at once in this country. Of 
these only 18 are classed as of the first magnitude, the brightest 
of which are Sirius, Canopus, Alpha Draconis, Arcturus, Eiga, Vega, 
Capella, and Aldebaran. Of the second magnitude there are between 
50 and 60 visible to us, and about 140 of the third. 

Though 5,000 is the greatest number of stars that can be seen 
with the naked eye there are visible through the best telescopea 
thousands of millions, the number seen being estimated at between 
four and five hundred thousand million. Those that can be seen 
with an ordinary good telescope number about twenty million, and 
of these eighteen million occur in what is known as the Milky Way, 
namely, that zone of faint light which stretches from the horizon on 
one side nearly over our heads to the horizon on the other side. 

As previously mentioned, these fixed stars, as they are termed, have 
motion similar to the planets and satellites of the solar system, and 
are kept in their relative positions by the same force, viz., gravita- 
tion, which binds the members of the solar system together. As a 
general rule it is found that the stars of the first and second mag- 
nitudes have the largest proper motion, though there are exceptions 
to this rule. Some of them have an annual motion proper of even 
as much as 8". The two stars of 61 Cygni, of the sixth magnitude, 
have an annual motion of 5g". The annual parallax — that is the 
angle which the radius of the earth's orbit subtends at the distance 
of the star— is about ^" of space = 206,265 x 3 = 618,795 times 
the radius of the earth's orbit, or distance from the sun --92 million 
X 618,795 = 56,929,140 million of miles. The probable nearest 
fixed star is Alpha Centauri, which subtends an angle of 1". Hence 
its distance is 206,265 times the radius of the earth's orbit = 
18,976,380 million miles. Another whose distance has been mea- 
sured is a Lyrce, the parallax of which is about one-fifth of a second, 
or five times the distance of the star a Centauri. Regarding the 



APPB^"DIx, 149 

Tnagnitude of the stars we liave no certain evidence at present, 
though astronomers believe that many are far superior in size to 
our sun. Thus, for instance, it has recently been made out that 
the masses of Sirius and his small companion are together nearly 
twenty times that of the sun ; and more extraordinary still is the 
case of Procyon, -which, with its small attendant, contains probably 
about ninety times the amount of matter in our sun. 

Though the stars are distant suns they are not all exactly like 
ours, as an examination of them shows. Among the very bright 
ones some appear to have more simple atmospheres than our lumin- 
ary — namely, they do not contain all the elements found in the sun. 
Among the stars which are not so bright — especially those whose light 
appears of a reddish hue — the atmosphere seems very diflferent from 
that of our sun. So much, indeed, that it is supposed that such 
stars are colder than our sun. 

135. Variable Stars. — One of the most interesting of the phe- 
nomena that is observable in the stars is that of the periodical 
variation of brilliancy belonging to some of them. Thus, in the time 
of Tycho, a star suddenly appeared in the constellation Cassiopeia, 
whose brightness exceeded that of stars of the first magnitude, and 
equal to that of Venus when nearest the earth. Its brightness 
decreased very rapidly, having died, as it were, entirely out in 
sixteen months. Some stars complete their period of variation in a 
very short time. For instance, Algol requires only 69 hours. During 
nine-tenths of the time it appears as a star of the second magnitude, 
and then changes till it becomes one of the fourth magnitude, 
the remaining one- tenth of the 69 hotu-s being taken up half in 
decreasing and half in increasing its brightness. Another remark- 
able instance is j3 Persei, whose period of change is about 2 days 
20 hours 49 minutes, during which time it varies in brightness from 
that of the second magnitude to the fourth, continuing in its 
brightest state for 2 days 13 hours, the remainder being occupied 
in decreasing and increasing. Another instance is d Cephei, whose 
period is 129 hours. /3 Lyrae's period is 156 hours. A Hst of 
between 200 and 250 have been collected. That observed by Tycho 
properly belongs to the "temporary" class, a remarkable one of 
which burst suddenly out in May, 1866, equal in brightness to the 
stars of the second magnitude, and declined from this to that of one 
of the twelfth magnitude in twelve days. Four days after the first 
appearance of this star Dr. Huggins and Dr. Miller examined the 
spectrum, which was found to consist of two distinct parts, or rather 
there were two distinct spectra, one of which was formed of four 
bright lines, and the other was analogous to those of the sun and 
stars. The bright lines in the spectra showed that it had its origin 
in incandescent gases, and the position of these lines showed that 



150 APPENDIX. 

hydrogen was one of these. Hence it is imagined that the star 
became suddenly enveloped in the flames of burning hydrogen. 

There is also another class of stars — namely, double and muUvple 
stars, the most remarkable of which are 61 Cygni and 7 Virginis in 
the Northern Hemisphere, and a Centauri in the southern. This class 
consists of those stars that go round each other, and are termed 
double, or multiple, according as there are two or more moving around 
each other. They are said to be physically connected with each 
other, being so close that one revolves round the other, as w© 
revolve round the sun. The shortest known of these periods of 
revolution is 36 years. The number of these systems at present 
known is 800. 

136. Colour of the Stars.— The colour of stars varies greatly, 
as when seen through a telescope some are red, some orange, or 
yellow, while the smaller companion stars generally appear blue, 
violet, green, &c. When they appear as double stars, or binary 
systems, the two are generally of different colours — namely, com- 
plementary. Thus, if the larger of the two be of a yellowish colour 
the lesser one will appear bluish, but if the colour of the former be 
crimson the latter will be of a greenish hue, and so on. 
Sir J. Herschel was of opinion that these colours might possibly not 
be the result of contrast, but of light differently tinted. 

Among the stars that are white may be mentioned Sirius and 
Capeila. Ruddy — ^Aldebaran and Antares. Yellow — Arcturus and 
Pollurft. Orange — /3 Cygni (the larger). Blue — ^ Cygni (the lesser). 
Bed — Betelgeux. 

137. Classification of Stars according to their Spectra.— 

The spectra of many of the fixed stars differ very little from that of 
the sun. Dr. Huggins devoted great attention to the spectrum of 
Sirius (the brightest of the fixed stars), which he found to be a 
continuous one, crossed by a number of dark lines, which are 
disposed at pretty equal intervals through its whole length. The 
series of colours correspond so far with that of the solar spectrum 
that the combination of the whole gives out a white light. The 
spectrum of this star corresponds with that of the sun by presenting 
four strong lines . The spectra of all the stars yet examined, with the 
exception of two, show the presence of hydrogen — viz., one of the chief 
constituents of the sun ; and sodium, calcium, iron, and magnesium 
are often recognised. In Aldebaran, bismuth, mercury, antimony, 
and tellurium have also been recognised. So that we may state 
generally that the fixed stars have a composition resembling that 
of the sun. An examination of the spectra shows that they generally 
are identical with that of the sun, though very minute differences 
have appeared. From these astronomers have been able to divide 
them into four classes or orders. The first includes those which shine 



APPENDIX. 15 1 

with a white light, which consists of the greatest number by far. 
These spectra show all the seven colours, crossed by the four lines of 
hydrogen and many others. The second class includes those whose 
light is yelloio, having spectra crossed by numerous fine dark lines, 
resembling those of the solar spectrum. This class is second in 
number to the white. The small remaining portion consists oi; 
orange and red stars, which form the third class. Their spectra 
have bright lines in as well as dark, and appear something like that 
of the spots of the sun. The fourth class consists of the third class 
arranged in band-s, and embracing the faint stars. 

THE PRINCIPLES OF THE SPECTRUM ANALYSIS. 

138. This analysis reveals the chemical elements of a hody hy 
the character of its spectricm xvhen reduced to a state of gloioing 
vapour. When a beam of solar or white light is caused to pass 
through a prism the beam is refracted, and also separated into 
its constituent parts, a phenomena which is called dispersion. 
Sir Isaac Newton admitted a sunbeam through a small circular aper- 
ture in the shutter of a darkened room. When there was nothing in 
the way to prevent it, the ray of light formed a straight line, causing 
an image on the floor ; but on making the beam to pass through a 
horizontal prism the rays were refracted, and formed on the wall or 
screen seven beams of colour, namely (commencing from the bottom) 
red 12, orange 7, yellow 12, green 27, blue 27, indigo 11, and violet 
33 — the numbers representing the proportionate parts of the colours 
in the spectrum. The elongated image on the screen is called the 
solar spectrum. Besides these coloured rays there is an invisible 
space below the red, where the heat is greater than in any other 
part, and a space above the violet, where the chemical effect is 
greater. The invisible rays below the red are termed heat rays, and 
those above the violet actinic rays. The yellow rays give the most 
Hght. 

On a careful examination through the telescope it will be observed 
that the different colours are crossed by a great number of dark 
lines, not absolutely black, but of different degrees of blackness. 
These are known as Frauenhofer's lines, so named from the German 
optician who first accurately observed and mapped out the position 
of 876 of them, in 1815. The real discoverer of these lines was our 
own countryman. Dr. Wollaston, in 1802, when he discovered two 
lines with his naked eyes. These Hues occur in groups of fine Unes, 
with an occasional thick one, their order being always the same. Of 
the more conspicuous lines Frauenhofer chose eight, which he 
denominated A, B, C, D, E, F, G, and H, to compare the rest with. 
A, B, and C are single dark lines in the red, D is a double line 
between the orange and the yellow, E a group of fine lines in tha 



152 APPENDIX. 

green, F a thick "black line at the commencement of the blue, and 
G and H two groups of fine lines in the indigo and violet. 

139. The Spectroscope is an instrument used for the purpose of 
analysing the rays of light from any luminous source. It consists 
chiefly of a series of prisms constructed of flint glass, to cause the 
beams of light to be dispersed. The more recent construction is to 
have a prism of crown glass, then a prism of flint glass, and so on, 
leaving a crown glass one last. This arrangement causes a minimum 
of deviation in the dispersed beam. On examiuing the spectra from 
different sources of light the following main results are obtained : 
(1) Solid and liquid bodies in a state of incandescence give out 
continuous spectra. (2) That glowing vapours and gases give out 
spectra with bright lines on a dark background, these lines being 
different for different substances. (3) When the light from any 
luminous body is caused to pass through a gas, such rays are absorbed 
hy the gas as it woidd itself emit when rendered incandescent. It is 
from the above three results that the constitution of the sun and 
other heavenly bodies has been obtained. Thus the vapour of 
silver, when incandescent and passing through a prism, gives a 
beautiful green Une across the spectrum. Sodium gives one bright 
yellow bar in exactly the same position of the dark Frauenhofer 
line which is in the yellow of the spectrum, the remainder of the 
spectrum being rendered dark by the primary colours being absorbed. 
As above stated each substance has its own characteristic line or 
group of lines, and even if it be a compound substance, each 
constituent will reveal its own line or lines, each in its own position — 
it being remarkable that these lines never interfere with each other in 
taking their position in the spectrum. 

The test for the presence of sodium is so delicate that the three 
millionth part of a milligram (about the two hundred millionth 
part of a grain) of a salt of sodium will colour the flame yellow and 
give the sodium Hne in the spectrum. On allowing an intense hght — 
for instance, the oxy-hydrogen lime-light — to send a ray through 
a prism, a spectrum is obtained containing no dark hne ; but on 
allowing this light to fall through a flame coloured by sodium 
chloride (common salt) the Frauenhofer line appears in the centre of 
the yellow. From this we draw the result (3) that the sodium 
flame has the property of absorbing the rays of the same colour 
which it sends out (yellow), and also that incandescent vapours and 
gases absorb the rays of the same colour which they emit. The 
light from the sun always shows these dark Hues. Hence it is 
inferred that the light before reaching us must have passed through 
the vapour of sodium, which must exist either in our atmosphere or in 
that of the sun ; and in like manner when we find that in the solar 
spectrum there are dark lines occupying the places of the bright 



APPE2IDIX. 153 

lines belonging to particular metals, we come to the conclusion that 
the sun is surrounded by a gaseous atmosphere which contains these 
metals in an incandescent state. In this way it has been proved 
that the sun's atmosphere contains, amongst others, the following 
metals in a state of vapour : Aluminium, sodium, iron, magnesium, 
cobalt, calcium, chromium, barium, copper, nickel, and also glowing 
hydrogen in great quantities. The protuberances seen round the 
edge of the sun during total eclipses are believed to be chiefly due 
to the presence of hydrogen. 

During total eclipses of the sun red protuberances, appearing in 
the shap of huge red flames, have been observed to appear to shoot 
from beneath the edge of the moon's disc to the height of eighty 
and even one himdred thousand miles. They were for many years 
supposed to belong to the moon, namely from 1706 to 1842, when 
that notion had rather a rough shaking by the total eclipse visible 
in France and Italy, observed by many scientific men ; and in the 
year 1860, these flames themselves, by the aid of Mr. De La Rue 
and artistic photography, told their own tale on his photographic 
plates, announcing themselves as belonging to the sun, and, more 
than this, giving us information regarding their extent (one of the 
prominences registered extended 7:ii,000 miles from the sun's surface 
into his atmosphere), and also what they must consist of. The 
exact position and extent of these prominences was recorded by 
photographs taken during the progress of the eclipse, and they were 
found to change so rapidly and remarkably as clearly to indicate 
that they consisted of luminous vapours. 

According to J. N. Lockyer, these red flames are local aggregations 
of an envelope (chromosphere), chiefly, consisting of hydrogen, which 
extends over the whole of the solar sphere to an average thickness 
of about 5,000 nnles. They undergo continual and often most 
rapid changes. For instance, Mr. Lockyer saw an outburst 27,000 
miles high, which disappeared entirely in less than ten minutes ; and 
far exceeding this is one described by Professor Zoller, which shot 
up as a tongue of flame 50,000 nules high, and he says he could 
scarcely believe his own eyes when he saw a sort of flickering motion 
in this flame, caused by the travelling of a flame-wave from its base 
to its point in the course of two or three seconds. At another time 
an immense cloud-like mass of incandescent hydrogen was seen 
resting on the top of a conical prominence. In a few hoiu-s after- 
wards this mass, greatly increased in size, was seen floating many 
thousands of miles above the prominence. It is believed that these 
extraordinary phenomena are, in a great measure, due to local 
variations of temperature sinular to those which produce storms, 
cyclones, &c., in our own atmosphere; but the difierences of tem- 
perature that cause the solar storms cannot be less (as Kirchhoff 
remarked) than thousands of degrees. 



154 • APPENDIX. 

The spectroscope also shows us what the spots on the sun's sur- 
face really are, namely, parts of the solar atmosphere in which the 
temperature of the glowing gases has undergone reduction, and that 
they appear to us black simply because they are less bright than the 
surrounding portions of the photosphere. The darkened area of the 
sun spot is an area of powerful absorption, produced by the density 
of the metallic vapours being increased, arising from a cooling of 
these vapours, which will produce a downward current, drawing 
them nearer to the sun's surface. Those bright stripes termed 
facidce are just the reverse, depending on their higher temperature, 
and producing a current in the opposite direction, viz., U2nvards. 

Still, more than this, the spectroscope has been applied to find the 
velocity with which the various vapours move about in that atmos- 
phere, Mr. Lockyer by the aid of this instrument determined the 
velocity of the rush of those currents of white-hot hydrogen. Thus, 
viewing the sun's surf ace through his spectroscope, he saw the Frauen- 
hofer line F (hydrogen line) appeared bent, sometimes by shifting at 
Beveral points towards the red end of the spectrum, and at other times 
by a displacement towards the violet end. Now the shif tings and' 
movements of this line indicate alterations in its wave-length, which 
diminish as the line moves towards the violet end and increase 
as it moves towards the red end. The displacement discerned was 
to the extent of one ten-millionth of a millimetre, showing that the 
incandescent hydrogen is rushing at the rate of 38 miles per second, 
Avhich equals 136,800 miles per hour — in the first case toivards the 
observer, but in the second case from him. Now these motions on 
the sun's surface must be upwards in the first case and downwards in 
the latter case, if the central 'part of its disc is under observation, as 
no movement along its surface will alter the distance of the moving 
body from the eye of the observer. But in viewing the limh* of the 
sun a motion of approach to, or recession from, the eye of the 
observer, will be one parallel to, or along, the sun's surface. 
These movements betoken storms which rage on the surface of the 
Sim. Thus, supposing a cyclone raging over a portion of the sun's 
disc, which we are viewing edgcioays, it is evident that the current 
will be toiuards us on one side and from us on the other. This will 
show itself in the direction of the F (hydrogen) line on the violet end 
of the spectrum on one side and towards the red end on the other. 
This reflection has been witnessed repeatedly. The lateral displace- 
ment of this line on one occasion was such that it made it appear 
treble. A portion of the hydrogen flame had no motion towards the 
observer, while others were approaching him at velocities increasing 
to the rate of 120 miles per second, or 432,000 miles per 
.hour. To comprehend the terrific violence of these storms 

* Border 



APPENDIX. 15|i 

of incandescent hydrogen we must remember that the greatest 
'Speed of the most violent hurricanes which occur on our globe 
is 100 miles an hour. (See 103.) Then what must be the 
storm which rages at the rate of 432,000 miles in the same 
time, or 431,900 miles more per hour ? The interior of each of 
these whirlwinds of flame is the spot. These spots have been 
shown to have a cycle of increase and diminution extending 
over a period of nearly eleven years, known as the sun-spot period. 
It has also been ascertained from facts collected by Mr. Meldrum, 
the astronomer at Mauritius, that the periodical maxima of these 
spots are those of the most numerous and violent hurricanes on 
our own globe, thereby leading us to suppose that our atmosphere 
is in some way connected with that of the sun. Further than this, 
evidence has been obtained by the spectroscope which suggests the 
existence of a very attenuated atmosphere between the sun and the 
earth, as bright bands, one of which seems identical with the third 
line of the corona* have been observed in the spectra of the aurora, 
of the zodiacal light, and even the phosphorescent glow seen at 
times over the general sm^face of the sky on a starlight night. 

140. NebulSG. — Not only has the spectrum analysis been applied 
to the solar system, but it has been extended far beyond, adducing, 
in the hands of Dr. Huggins and others, evidence regarding the 
present conditions of non-terrestrial matter, and throAving much light 
on what is termed the nebular hypothesis. Nebulce is the name given 
to the system of stars which appear as little clouds of self-luminous 
matter of very httle density, being in a highly gaseous state. These 
are scattered in all directions in the remote heavens. 

The nebulae (of which nearly four thousand are known) are of two 
classes, some appearing, by the aid of powerful telescopes, as immense 
clusters of stars, termed resolvable, while others appear, even by the 
aid of these telescopes, luminous mists or gases, and are termed 
irresolvable. In the first class the spectra exhibited are similar 
to the sun and the other planets, and in the spectra of the latter 
class are found three bright lines — one of hydrogen, one of nitrogen, 
and the third is as yet undetermined. 

Now if this latter class had been a cluster of stars its spectrum would 
have been continuous, hke that of a single star, though extremely 
faint. Hence Dr. Huggins concluded that the spectrum was not 
formed like that of the sun or stars, by light proceeding from a white- 



* (See 59.) The extent of this is such that distinct indications of its 
photographic action have been obtained at a distance of nearly two million 
mUes from the surface of the sun. The inner part gives three bright lines on 
a faint continuous spectrum— two showing the presence of incandescent 
hydrogen, the third indicating some other substance. 



15€ APPENDIX. 

hot nucleus enveloped in an atmosphere whose absorptive power 
converts its bright lines into dark ones, but ly luminous matter in a 
gaseous condition. Dr. Huggins examined one nebula after another, 
and found that they might all be distinctly separated into two 
groups — those giving a spectrum consisting of three bright lines, 
which are gaseous, and those giving a continxious spectrum, which 
are therefore stellar. Regarding the chemical constitution, two out 
of the three lines are characteristic of hydrogen and nitrogen. 

141. The Nebular Hypothesis.— The hypothesis of Kant, the 

great German philosopher, was that all the planetary bodies of the 
Bolar system rotating and revolving in the same direction appear to 
have been created together, and that their motion was given to them 
by a single impulse. Other hypotheses have been suggested, the 
chief of which is that of Sir W. Herschel, which supposes that all 
sidereal bodies are continually growing, and other bodies forming 
from the aggregation of nebulous matter. Thus a nebula in its first 
stage gets continually smaller and rounder, getting hotter and hotter 
all the time, and condensing and contracting until it becomes a 
nebulous star, leaving rings of vapour round its equator like those of 
Saturn, eventually breaking and forming a globular mass of vapour, 
which gradually cools until at last it becomes a planet. As the rate 
of contraction diminishes it shines like a sun, giving light and heat 
to planets like ours that have become cool and habitable. These 
stars, after shining first as bright stars, gradually lose their bright- 
ness, becoming dim or, perhaps, red, as in the case of Jupiter and 
Saturn, which have the appearance of expiring suns, no longer 
shining with their former vigour. 

In concluding the present notice of the spectrum analysis we 
cannot do better than give a summary of the facts elicited by 
Dr. Huggins' s investigations in his own words : — 

(1) " All the bright stars at least have a structure analogous to 
that of the sun." 

(2) "The stars contain material elements common to the sun. 
and earth." 

(3) " The colours of the stars have their origin in the chemical 
constitution of the atmosphere which surrounds them." 

(4) " The changes in brightness of some of the variable stars are 
attended with changes in the lines of absorption of the spectra." 

(5) " The phenomena of the star in Corona appear to show that, 
in this object at least, great physical changes are in operation." 

(6) "There exist in the heavens true nebulae. The objects 
consist of luminous gas." 

(7) " The material of comets is very similar to the matter of the 
gaseous nebulae, and may be identical with it." 

(8) " The bright points of the star-clusters may not be in all cases 
stars of the same order as the separate bright stars." 



APPENDIX. 157 

LATITUDE AND LONGITUDE. 

If we know the latitude and longitude of any place we know its 
exact position, but if only one of the two is known its position is 
undeterminable, as thousands of places have the same latitude or the 
same longitude, but not both. So we see both are necessary. In lati- 
tude all nations measure from the equator, but longitude is measured 
from many places. Thus, we reckon from Greenwich ; therefore one 
half of the world will be east, and the other half west. Hence the 
longitude of any place cannot exceed 180°, namely haK of 360°, the 
circumference of a circle. Now comes the question : ffow can the 
latitude and longitude ie found? We will try to make this plain, but 
first the student must understand the terms used, short definitions 
of which we here give : — 

The position of a heavenly body is generally referred to two great 
circles drawn on the celestial concave, namely, the celestial equator 
and the ecliptic. The celestial pole is the point in the heavens which 
the axis of the earth would reach, prolonged, and round which the 
stars appear to move. The celestial equator is a circle described on 
the heavens by the plane of the earth's equator produced ; the zenith 
is the point of the heavens exactly over the observer's head, and 
nadir the point in the celestial concave exactly opposite his feet. 
The horizon is of three descriptions, namely, sensible, rational, and 
visible or apparent. The sensible horizon is shown by a plane touching 
the earth at the spectator's feet, and there extended to the celestial 
concave. The rational horizon is shown by a plane through the 
centre of the earth drawn parallel to the visible horizon and cutting 
the sky. The visible horizon is where the sky and earth appear to 
meet, forming a circle round the spectator, of which he is the centre. 
The altitude of an heavenly body is the angular distance of that 
body from the horizon, measured on a verticle circle. 

142. The Latitude of an observer may be found by the altitude of 
any celestial object when on the meridian*. Thus, the sextantt being 
placed in a vertical position, the upper or lower limb of the sun, by 
moving the index, is brought down to the horizon. Seen directly, 
this index shows the altitude. The sun is known to be on the 
meridian when it ceases to rise higher, or when the index angle 
ceases to increase. The latitude is always equal to the sum or 
difference of the zenith distance and decimation — the zenith 
distance being always 90° altitude, and the declination, or the position 
of the sun and principal stars from the celestial equator, is given in 
the " Nautical Almanack." Hence the latitude is easily known. 

* Every place is supposed to have a meridian passing thro\igh it, and 
^hen the sun comes to that meridian it is noon, or midday, at that place. 

t SextoMt, so called on accoimt of consisting principally of a sixth part of a 
circle or an arc of 60'. 



158 APPENDIX. 

Rules when to Add and -when to Subtract. — If the zenith 
distance and declination are loth north or both south add for the 
latitude ; hut if one he north and the other south their difference is 
the latitude. When hoth are north or south then the latitude is north 
or south ; if one is north and the other south the latitude is of the 
tame name as the greater. 

Another method of obtaining the latitude is to measure the 
altitude of the pole star. Thus, if we were at the equator the north 
or pole star would appear on the horizon, its altitude being 0° ; but 
supposing we travel northwards for 206 mUes we should find its 
altitude 3°, which is the latitude. In like manner, if at a certain place 
it appeared 40° above the horizon, then the latitude of that place 
is 40°. This is supposing the pole star continually due north, which 
is not quite correct, it being always about l^°from the pole. Hence, 
correction should be made for this. 

Other methods are — (1) By observing the altitude of a star when 
on the meridian, and calculating the latitude from its own distance 
from the polar star. (2) By taking half the sum of the greatest 
and least altitudes of a circumpolar star. 

143. Longitude. — The earth makes one revolution on its axis 
every 24 hours. Hence if the sun or star is on the meridian 
at any place it will be on the meridian of another place 
(360°-=- 24) 15° west of the first in one hour. It is on this fact that 
aU methods of calculating the longitude are based. The difiference in 
time at two places at the same moment gives the number of degrees 
of longitude they are apart, every four minutes' difference corre- 
sponding to 1°. To find the time of day, termed local, at the place 
of observation, all that is necessary is to observe the moment when 
the sun crosses the meridian, it then being 12 o'clock; and then, 
glancing at a watch or chronometer that is carefully set to Greenwich 
time,* the difierence between the two gives the longitude. Thus, if 
the watch shows half -past one then the place is 15° x 1^ = 22^° W. 
Had the Greenwich time been earlier than that of the place, say 
11 o'clock, then the longitude would have been 15° x 1 = 15° E. of 
Greenwich. Other methods are — (1) In the " Nautical Almanack" 
the Greenwich time at which the moon is at certain distances from 
certain stars is given. Mariners note the local time (as above) at 
which the moon is at the same distances from these stars, and so the 
longitude is known. (2) The eclipses of Jupiter's satellites are seen 
by all observers in all parts of the globe at the same instant. These 

* Many ways have been tried so that the correct Greenwich time may be 
known, as no watch or clock can keep apparent time. When telegraph wires 
are laid from one place to another the time of either place may be easily 
known at the other. On sea chronometers are used, which answer for a 
short time ; but methods have to be resorted to to check them, as they are 
liable to variation. 



APPENDIX. 159 

exact times of occtirring are given in the ''Nautical Almanack" a long 
time beforeliand — namely, Greenwich time. Hence the difference 
between the local time of occurrence and the given Greenwich time 
is the longitude in time. Thus, suppose the eclipse is to take place at 
2h. 15m. p.m., Greenvdch time, and at the observed place it takes 
place at 4h. 55m. p.m., then the difference, namely, 2h. 40m, = the 
longitude in time = 160m., but 4m. = l°.-.lon^tude = 160-f4=40° 
east of Greenwich. Observations of lunar transits, and the occulta- 
tions of fixed stars, afford the means of determining longitude. 

As the parallels get smaller towards the poles it is evident that 
the degrees of longitude, which are 69| statute miles long at the 
equator, get shorter towards the poles. At all places of the same 
latitude the length of a degree of longitude is the same. To find the 
length of a degree of longitude at any place multiply the cosine of 
the latitude by 69|. Thus, suppose the latitude is 29° 55' the cosine 
(see "Trigonometrical Tables") is •8663161. Hence a degree of 
longitude = -8663161 x 69-5 = 60-2089 miles. 

MAP PROJECTIONS AND GEODETICAL SURVEYS. 

There are several methods of projections of maps of the earth, the 
(Chief of which are the stereograpkic, globular, orthographic, conical, 
tylindrical or M creator's. It is evident that the surface of the earth 
can be best represented by means of the artificial globe ; but, o^ang 
to the vast difference in the diameters even of the largest th?vt can 
be made, the minute features cannot be detailed, so that we must 
have recourse to maps, or plane representations of a sphere or any 
part of it, exhibiting the countries, seas, rivers, mountains, cities, 
towns, and their positions, &c. In the stereographic, globular, and 
orthographic the plane of projection — that is the flat surface on 
which the map is drawn — is supposed to pass through the centre of 
the earth. 

The Stereographic Projection is generally adopted for maps of the 
hemispheres, the eye of the observer being presumed to be at the 
surface of the globe, exactly opposite its centre. In this projection 
a disadvantage occurs, the maps not being correctly drawn, as every 
part from the outHne to the centre is gradually contracted. The 
following is an example of the method in which maps of this 
description are projected or drawn. The student should draw the 
figure for himself as described. 

144. Projection of a Map of the Earth on the Plane 

of a Meridian. — First, draw the circles of latitude thus : 
Describe a circle, A B C D, of any magnitude, representing one 
hemisphere, or half the surface of the earth. Draw the diameters. 
A C and B D, intersecting each other at right angles. Then A C 



160 APPENDIX. 

represents the axis and B D the equator. Divide the circumference 
into 36 equal parts of 10° each, viz., 10, 20, 30, &c. (or into smaller 
parts if the circle is large enough to admit of it), commencing at 
the north pole. A, and proceeding to the right hand, so tbat it is 
90atB, 180 ate, 270 at D, &c. From D draw a line to 110, 
cutting A C at a. Bisect the part between a and 110 atv, and from 
this point raise a perpendicular, v x, producing it till it cuts A C 
extended on x. This point x will be the centre and x a the radius 
of the circle to describe the parallel of 20° south latitude. In a 
similar manner describe the parallel for every 10°, or for every degree 
if required. To obtain those in the Northern Hemisphere set oft 
on the line C A, produced in the opposite direction, the distances 
C X, &c. These give the centres on which the circles of latitude are 
to be described for every 10° in that hemisphere. Secondly, draw 
the circles of longitude. By lines drawn from C to 10, 20, .30, &c., 
in the quadrant A B, the radius B (O being the centre of the 
circle) will be cut at the points 1, 2, 3, 4, 5, 6, 7, 8. Then the points 
at 2, 4, 6, 8, will be the centres on which the circles of longitude are 
to be drawn. The remaining circles must be drawn as follows: 
Produce the diameter D C, and from A, through every tenth degree 
in the quadrant A B, draw lines cutting the diameter produced, and 
the points of intersection will give the centres for the remaining 
circles ; but it must be remembered that each centre is 20° apart. 
In a similar manner the lines for the other haK of the hemisphere 
are drawn. Other stereographic projections are drawn on the plane 
of the equator and the horizontal projection. 

The Globular Projection was devised to remedy the defect of the 
preceding projection, namely, that of contracting the centre and 
enlai'ging the marginal portion of the map. It is now used by many 
geographers. By this method equal spaces on the earth are repre- 
sented by equal spaces on the map, as nearly as possible ; but it 
must be remembered that it is impossible for a spherical surface to 
be exactly represented upon a plane. In this projection the point 
of view is supposed to be vertically over the centre of the plane of 
projection, and at a distance from the surface of the sphere equal to 
the sine of 45° of one of its great circles. The following is the method 
of drawing a map of the earth on the plane of a meridian by this 
projection : (1) Take the same circle and diameters as in the pre- 
vious example. Then divide the quadrant B C into nine equal 
parts, 10, 20, 30, &c. From D to each of these divisions draw right 
lines, as D a 20, D & 30, D c 40, &c. Then divide these hues— 
namely, the part in the quadrant B C — into two equal parts at 
d. From this point let fall the perpendiculars d! E, tZ G, c? F, 
&c., produced till they cut the polar diameter A C, and extended 
to A C H (or indefinitely). The points E G F are the cen- 
tres from which the circles of latitude for 20, 30, and 4® 



APPEXDIX. 161 

degrees are drawn, the radii being E a, F a, H a, &c. ; a being the 
point at which the lines drawn from D cut the polar diameter. 
In a similar manner draw the parallels for every 10° or degree ii 
required. To obtain those for the Northern Hemisphere the 
simplest way is to turn the north part of the map to the place of 
the south, and proceed as before. (2) To draw the circles oi 
longitude, divide the quadrant A D into nine equal parts, 10, 20, 
30, &c., and the quadrant C D into two equal parts of 45° each, and 
let fall a perpendicular Hne from these points to the polar diameter 
A C at f . Set off on this diameter produced, C x, equal to s ^ ; then 
lines drawn from x to 10, 20, 30, &c., in the quadrant A D, will 
divide the radius D in the points 1, 2, 3, 4, 5, 6, 7, 8, through 
which the radii of longitude are to be drawn. It is now requisite 
to find the centre through which these circles may be drawn. This 
may be done as follows : To find the radius of the circle of 
longitude A 3 D, join the points A 3 and D 3 ; divide these two 
lines each into two equal parts in s, and let fall the perpendicular 
lines, and the point of intersection is the centre of the circle. The 
other centres may be found in a similar manner. 

In the orthographic projections all the parallels are in planes 
perpendicular to the plane of projection, being represented on the 
map by straight lines, all the meridians except the one in the centre 
appearing as elliptical curves. This method has the disadvantage 
of contracting the outer parts or margins of the map. Hence it 
is not generally used, though modifications of it are used for the 
maps of Africa and South America. 

As the three projections above described are only adapted to 
the construction of maps of the world, some other method had 
to be devised for drawing maps of individual countries or continents. 
This method is termed — 

The Conical. — In this projection all the parallels of latitude are 
arcs of circles drawn from a common centre — namely the apex of the 
cone — the meridians being straight lines projected from the same 
point. This projection is well suited for maps of countries, as 
Europe, Asia, North America, &c. Thus, for example, in drawing 
the map of Europe it is found that the common centre of all the 
parallels of latitude is at 6 '7° beyond the pole. Draw a line for the 
central meridian of the map, and assume any distance for 10° ; set 
off six times and the sixth extreme will be the pole, and 67 degrees 
more laid down beyond it wiU be the common centre of all the 
parallels, which may at once be drawn. To draw the meridians, 
take the number of miles in a degree of 30° latitude, namely 51*96 
miles; set this off on each side of the central meridian on the 
parallel or circle of 30° of latitude. From these points of division 
draw right lines to the common centre or apex of the cone, and they 
will represent the meridians, 
L 



162 .APPENDIX. 

Mercator*s, or Cylindrical Projection. — This projection was devised 
by Gerard Kauffman, to facilitate the laying down of courses on the 
sea, enabling the mariner, while steering by his compass, to work 
•with straight lines only, the meridians and latitude circles being 
represented in parallel straight lines. This projection is drawn on 
the circumscribing cylinder of a sphere (the area of a sphere is equal 
to the convex area of the cylinder circumscribing it), the eye being 
supposed to be at the centre of the sphere. A map of this projection 
is constructed thus : A line of any length is drawn to represent the 
equator. This is divided into 36 or 18 equal parts for meridians, at 
10° or 20° apart, and the meridians are then drawn through these 
perpendicular to the equator. From a table of meridianal parts (a 
table of the number of minutes of a degree of longitude at the equator 
comprised between that and every parallel of latitude up to 89°) 
take the distances of the parallels and of the tropics and arctic circles 
from the equator, and mark them off above and below it ; then join 
these points, and the projection is complete. There is one disad- 
vantage of this method, namely, the gradual enlargement of the 
parallels as they recede from the equator, causing all countries in 
the high latitudes to be greatly distorted. Hence these maps do 
not usually extend beyond latitude 75° ; but this circumstance does 
not usixally detract much from their great value and usefulness to 
the mariner, and even to the student of physiography. 

145. Geodetical Surveys. — Before describing the method of the 
geodetical surveys we shall first describe the theodolite, the chief and 
foremost of the instruments used. It is used for measuring horizontal 
angles, and consists, in its simplest state, of a pillar turning freely 
on a vertical axis, carrying, on outiiders with Y supports attached, a 
telescope, mounted like a transit instrument, capable of being directed 
to any point. It has a graduated horizontal circle, parallel to the 
horizon, read by verniers carried by the vertical pillar. There is 
also a semicircular arc fixed to the Yj fo^' taking the vertical angles, 
so that at the same time both the horizontal angles subtended 
by each of the two points observed with it, and the angles of 
elevation of the points from the point of observation, can be taken. 

We cannot, it is evident, measure at once the whole surface of the 
earth, but we can measure by degrees tolerably large portions 
of its surface in various situations, and then, by calculation, the 
whole circumference and area ; or, to find its circumference, a 
degree of latitude is measured — that is, the length of an arc of a 
terrestrial meridian, the latitudes of the extremities of which differ by 
®ne degree. Thus the difference of latitude of two places in nearly the 
same meridian is to be ascertained by celestial observations, and their 
distance by terrestrial measurement. A horizontal base line of a few 
miles in" length is to be selected with ^reat care oyer a level tract .of 



APPENDIX. 163 

country — as for instance, the Lougli Foyle base line, in Ireland. 
Accurately measured this line then forms the basis for a large triangu- 
lation of the country to be surveyed. Conspicuous objects, on 
summits of hills, if possible, within sight, are then selected, and the 
angles which the lines joining them and the extremities of the base 
(viz., the measured line) make with its direction are accurately 
measured with the aid of the theodolite. Having two of the angles, 
the third angle may be found by adding these two together, and sub- 
tracting their sum from two right angles, or 180°. Now, we have all 
the data that is requisite for finding the lengths of the remaining two 
sides of the triangle, and hence its area, as, by knowing the angles 
of any triangle, we know their relative or -proportionate lerifjths, so 
that when one side is known the other sides are easily calculated.* 
In surveying very large triangles on the earth's surface, and 
measuring each of the angles to avoid the slightest error, and also as 
a check to see if the two angles obtained are correct, it is always 
found that the sum of the three angles is greater than txvo right angles, 
which could not occur if the earth was a plane flat surface ; but 
those of our readers .who are conversant with spherical trigonometry 
know that this is always the case in all spherical triangles — ^the 
dijfference being a measure of the spherical area, known by the 
name of the spherical excess. Hence we have a proof that the 
earth must be a sphere. A series of triangles are measured across a 
country in the direction of a meridian, forming, as it were, a 
network on its surface. By these means a degree of latitude is 
measured, and from thence the circumference calculated, (For the 
latest results, see 62.) For the purpose of measuring the curvature 
of the earth, degrees of meridian at diflferent latitudes, have been 
measured. Now if the earth was a perfect sphere it is evident that 
these degrees would be equal ; but such is not the case. Hence 
the earth is not spherical. But the difl&culty is to find the difference 
in the two diameters. The following is a very useful rule in 
determining the two diameters approximately : Having given the 
lengths of the arcs of the meridian corresponding to two given 
latitudes, divide each arc measured by the number of degi-ees and 
parts in it. Call the greatest quotient the first term, the other the 
Becond, and the difference is the third term. Then, to double the 
third term, add three times the second multiplied by the square 
of the sine of the latitude nearest the equator corresponding 
to the first term and divided by the square of the radius. From the 
sum subtract three times the first term multiplied by the square of 

*Let a be the side measured, 6, &c., the other sides ; also let A and B he the 
ohserved angles ; then the third angle (180°- A+B)=say C ; then it is easy to 
prove by trigonometry that 6 = ^sinJB ^^^ ^ _ g_ sin. C . ^^^ ^j which ara 

sin. A sm. A 

adapted to logarithmic computation. 



164 APPENDIX. 

the sine of the less latitude corresponding to the second term divided 
by the square of the radius. Call this result the fourth term. 
Then, as the fourth term : third term : : equatorial diameter : dif- 
ference of the two diameters (equatorial and polar). Divide the 
third term by the fourth, and call the quotient the fifth term. 
Multiply three times the fifth term by the square of the least 
latitude corresponding to the first or second. To this add 1, and 
from the sum deduct twice the fifth term. Call this last result the 
sixth term. Then, as the sixth term : 2 : : first or second (accord- 
ing to which latitude has been used) : seventh term, which is the 
length of 2° on the equator. Multiply this by 57"29578, and the 
answer is the equatorial diameter. For the polar diameter diminish 
the equatorial one by the product of itself and the fifth term.* 

The figure of the earth has also been investigated on the prin- 
ciples of hydrostatics. Considering the earth to have been originally 
a fluid mass, and taking the only force concerned to be gravity, Sir 
Isaac Newton came to the conclusion from the consideration of this 
force that the diameters were as 289 : 288. 

INSTRUMENTS. 

146. The TeleSCOpe.t — Of all the instruments used in the 
scientific investigation of the heavenly bodies the chief and foremost 
is the telescope — an instrument used to magnify objects, or to 
present their images under a larger angle than the objects themselves 
subtend, and likewise to render objects visible which would other- 
wise be invisible. 

The simplest form of an astronomical telescope consists of a 
double-convex lens, J placed at one end of a tube, six inches longer 
than the focal length of the lens. An image then appears in the air, 
within the tube, six inches from the end where the eye is placed, 
and is seen as a new object. 

The apparent size of an object is magnified when, instead of the 
object itself, we view the image formed by a lens. For instance, if 
the object viewed was distance 6,000 feet, and the focal length of 
the lens 6 feet, the image will be to the object as 6 : 6,000 — that is, 

* The student sho'old work the following example out for himself: The 
arc of meridian measured from lat, 30° to 31* is 68 878 miles, and the arc of 
meridian from lat 45" to 46' is 69 '047 mile*. Find the diameters, and from 
thence the compression. Ans. E., 7925'15 ; P., 7799'25. Compression ,J^. 

t Tele, afar off. Scopeo, I view. 

i A lens is a nudium bounded by two spherical siuf aces having a common 
axis, or by a spherical surface and a plane one. The forms which media are 
most usually made to assume for the purpose of refraction are— the parallel 
plate, the triangular prism, the sphere, the double-convex lens, the plano- 
convex lens, the double-concave lens, the plano-coixcave lens, the meniscufi^ 
and the concavo-convex lens. 



1 



APPENDIX. 165 

1,000 times less ; but as this image may be considered as a new 
object viewed by the eye at a distance of 6 inches, the smallest 
distance at which we can obtain distinct vision, instead of 6,000 feet, 
the angle under which it is seen is greater, and also the image is as 
much larger when seen at 6 inches, as 6,000 feet is to 6 inches or 
half a foot = 12,000 times ; but it is 1,000 times less than the object. 
Hence it is equal to the object divided by 1,000 and multiphed by 
12,000, or 12 times as large as the object, so that its entire surface 
is increased 12'^ = 144 times. 

The above is a refracting telescope. "We will now describe the 
reflecting telescope, of which there are four kinds — the Newtonian, 
the Gregorian, the Cassegrainian, and HerscheKan. 

The Newtonian consists of a concave object-speculum or mirror, 
a plane reflector, making an angle of 45° with the axis of the 
telescope, placed between the object-speculum and its focus*, and 
an eyepiece. Thepencilst of light from an object at a distance tend 
to form an image after reflection at the object-speculum, but are 
bent by the plane reflector, so that it is formed on the axis of 
the eye-piece and in the focus of the eye-lens. 

The Gregorian telescope consists of a large concave mirror, 
containing an aperture in the middle and placed within a tube ; a 
smaller concave mirror is fixed in the axis of the larger and at a 
distance from it, equal to a little more than the sum of their total 
lengths. Near the end of the smaller tube are two plano-convex 
eye-lenses, with the plane side towards the eye. The pencils of light 
proceeding from a distant object, after reflection at the object- 
speculum, form an inverted image of the object at the focus of this 
speculum, and after reflection again at the small speculum, form 
a second image inverted with respect to the former, and erect with 
respect to the object. 

The Cassegrainian telescope has a small convex instead of concave 
mirror, which is placed at a distance from the larger mirror, equal to 
the difference of their focal length. 

;: The following is a convenient way of ascertaining the magnifying 
'power of reflectors : Multiply the focal distance of the larger mirror 
J hy the distance of the smaller one from the image ; also multiply the 
^ focal distance of the small mirror' hy the focal distance of the eye-glass; 
then divide the greater of these products by the lesser^ and the quotient 
sis the magnifying power. 

^_ The telescopes of Herschel and of Lord Eosse dispense with the 
Ismaller mirror by inclining the larger one slightly, so as to throw 
the image on one side, when it is viewed by the eye-glass. They are 
the two largest that have been constructed. Of Sir W. Herschel'a 

l6T- 

-r- '• The focus is a point towards which rays converge. 

t The pencil of rays is a portion of light distinct from the rest. 



166 APPENDIX. 

the diameter of the speculum, or mirror, was 4 feet, its weight 
2,1181b., and its focal distance 40 feet. The diameter of the speculum 
of Lord Kosse's is 6 feet, and its focal distance 56 feet, diameter of 
the tube 7 feet, and the weight of the tube and speculum more than 
14 tons, the speculum being 4 tons. The cost of this instrument 
was £12,000. 

Another optical instrument of great value is the microscope, an 
instrument for magnifying minute, but accessible, objects. A 
single microscope consists simply of a convex lens, commonly called 
a magnifying gla?s, in the focus of which the object is placed and 
through which it is viewed. 

The solar microscope is a microscope with a mirror attached to it 
on a movable joint, which can be adjusted so as to receive the sun's 
rays and reflect them upon the object. It consists of a tube, a 
mirror, and two convex lenses. The rays of the sun are reflected by 
the mirror through the tube upon the object, the image of which is 
thrown upon a white screen placed at a distance to receive it. 

Of the other optical instruments, only one needs mention here, 
and that is the spectroscope, an instrument which reveals to us the 
nature and constitution of the heavenly bodies. (See 139.) 

146. Among the instruments used in magnetic olservattom 
the chief are, the declinometer, the bifilar, or horizontal force 
magnetometer, and the balanced or vertical force magnetometer. 
The declinometer consists of a bar-magnet, freely suspended by a 
bundle of untwisted silk fibres. The variations of the positions of 
this magnet correspond with those of the vertical plane in which 
the earth's force is exerted. The Nfilar is a similar bar-magnet to 
the above, suspended by two nearly parallel bundles of fibre, slightly 
separated. The double point of suspension is twisted round until 
the bar is in a position perpendicular to the magnetic meridian. It 
is then kept in this position by two equal forces acting in opposition, 
namely, the gravity of the bar and its appendages, which tend to 
untwist the skeins upon which it is suspended, and the horizontal 
component of the earth's force, tending with an equal force to turn 
the bar in the opposite direction. Now the former force always 
remains constant, hence any variations of the latter force will produce 
corresponding variations in the position of the magnet, so tbat by 
observing these variations or changes of position, the variations of 
the horizontal magnetic force are determined. 

The third of these instruments — the balanced magnetometer— is 
a bar-magnet, very delicately poised on knife edges, so that it can 
move in a vertical plane, something similar to the beam of a balance. 
It is placed at an angle of 90 degrees (right angle) to the magnetic 
meridian, being kept in a horizontal position by a weight, which 
counteracts the tendency of the earth's vertical force to place it in a 



.APPENDIX. 167 ; 

vertical position. Now, as this is constant, it is evident tliat any 
changes in the amotmt of the vertical force would be shown by 
corresponding changes in the magnet's position. 

The indications of these instruments were formerly observed by 
viewing the divisions of a fixed scale reflected by a plane mirror 
attached to each of the magnets, through a telescope, which reqiiired 
observations to be taken at least every two hours, night and day, to 
furnish us with anything like a correct register of these variations. 
Hence the necessity of some other mode of registration — the best of 
which must evidently be the one that will cause it to register its 
own changes. This has been accomplished by the aid of photography, 
so that we have now an uninterrupted and faithful record of these 
magnetic changes, at the Royal Observatory, Greenwich. The mean 
elements for this year (1881) are mean declination, or variation of 
the compass, IS^SO'W. ; inclination, or dip, 67° 39'; intensity, or 
mean horizontal force (in British units), 3"9. The true or astro- 
nomical north can be found from the magnetic thus : Take the 
compass on a level surface, and turn the card round until the 
marked end of the needle poiuts 18°30' towards the west ; then the 
zero point of the card will be in the direction of the true or astro- 
nomical north, while the needle itself wiU be pointing to the mag- 
netic north. 

The method of photographic registration is thus : A concave 
metallic mirror, 3 inches in diameter, is attached to each of the 
three magnets hj a frame possessing all requisite adjustments, &c. 
The rays of light from a gas-burner, which is placed about 2 feet 
from the mirror, pass through a small aperture in a metallic plate, 
and fall on the mirror, from which they are reflected to a focus 
about 9 feet distant. As the source of light is fixed, the movements 
of the focal point of light will correspond with the movements of 
the magnet. A cylinder, covered with prepared photographic paper, 
is placed so that the point of Hght may fall on it, the axis of the 
cylinder being parallel to the focal point's motion. This cylinder ia 
continually being turned round on its axis by clock-work, and by 
the movements of the point of light and of the cylinder combined 
the magnetic curve is traced on sensitive paper. 



168 APPENDIX. 

THE NEBULAE HYPOTHESIS ; OR THE ORIGIN 
OF THE EARTH. 

TA paper by the author, which was published in the London University 
Magazine, 1879.] 

It may be inferred from the title of the present paper that hoio 
and when the earth was formed is now definitely known. We may 
reply, " Not yet," but perhaps at some future date science may be 
able to reveal the fact. Every day we seem to obtain some 
additional truths regarding our own and the other planets ; science 
now proving the *' identity of the constituents of the earth with 
those of the heavenly bodies." The object of this paper is to state 
in simple language how this knowledge has been obtained, and the 
conclusions that have been drawn therefrom. 

The science of chemistry has shown that this earth is composed of 
sixty-five elements or elementary substances, and of these, only 
about seventeen occur extensively, namely — oxygen, hydrogen, 
carbon, sulphur, silicon, boron, aluminium, chlorine, calcium, 
magnesium, iron, sodium, potassium, fluorine, lithium, and man- 
ganese ; these, combined in various ways, compose the greater part 
of the earth and its fluid envelope ; the others are of such rare 
occurrence as to be interesting only from a chemical point of view. 

Of these seventeen elements, several have been proved to exist in 
the sun, the centre of our universe — i.e., the solar system. This 
knowledge has been derived from the aid of the spectroscope — an 
instrument used for the purpose of analyzing the rays of light from 
any luminous source. It consists of a series of prisms of flint glass, 
which cause the rays to be dispersed, and which thereby reveal the 
chemical elements of a body by the character of its spectrum, when 
reduced to a state of glowing vapour. 

A beam of light in passing through a prism is broken up 
into its constituent parts ; thus, a sunbeam admitted through 
a crack in the shutter in a dark room, forms a straight 
line, and causes an image to appear on the floor, but, on 
the beam passing through a horizontal prism, the rays are 
refracted, and form on the wall or screen seven beams of colour, 
namely (beginning at the lowest), red, orange, yellow, green, blue, 
indigo, and violet ; this is what is termed the solar spectrum, and 
the seven colours are the constituents of white light. Supposing, 
instead of white light, we use a coloured one — for instance — such 



APPENDIX. 169 

as that emitted by burning sodium ; the colour of the spectrum is 
yellow, or the same as the light emitted by the sodium ; but, if a 
beam of white light is made to pass through this yellow light, there 
appears a spectrum consisting of seven colours as before, and in 
precisely the place of the yellow sodium spectra appears a dark band. 
Or, again, if the vapour of sUver, when incandescent, passes through 
a prism, it gives a beautiful green line across the spectrum ; and in a 
similar manner, if a beam of white or solar light is made to pass 
through, there appear the seven colours, and a dark line in exactly 
the place of the green one ; hence, it appears that the burning 
sodium and silver each absorbs the same rays as it emits, and only 
its own less luminous rays fall upon that part of the spectrum 
appearing as dark bands. Examining the spectra in this way from 
different sources of Hght, the following main results are obtained : — 

(1) Liquid and solid bodies, in a state af incandescence, give out 
continuous spectra. 

(2) Glotoing vapours and gases give out spectra with bright lines on a 
darTc hacJcground, and these lines are different for different sub- 
stances. 

(3) When the light from any luminous body is caused to pass through 
a gas, suck rays are absorbed by the gas as it would itself emit 
when rendered incandescent. 

So we see, each substance has its own characteristic line, or 
groups of lines ; even if the substance is a compound, each con- 
stituent will reveal its own peculiar line or lines, and thereby, by 
minutely examining the spectrum, the elements may be ascertained. 

It is by means of this " spectrum analysis " that the composition 
of the sun and other heavenly bodies has been obtained. Thus, 
suppose the spectroscope arranged so that the light from a sodium 
flame might pass through the lower part of the sHt, and a stmbeam 
through the upper part, and compare their spectra ; then introduce 
in succession the flames of hydrogen, iron, copper, &c., and if we 
find that in the solar spectrum there are dark Hues occupying the 
bright Hnes of these particular metals, we come to the conclusion 
that the sun is surrounded by a gaseous envelope or atmosphere 
which contains these metals in an incandescent state, and, con- 
tinuing in this manner, it has been proved that the sim's atmosphere 
contains, amongst others, the following metals in a state of vapour ; 
sodium, iron, nickel, aluminium, zinc, cobalt, magnesium, copper, 
barium, chromium, calcium, and immense quantities of glowing 
hydrogen. 



170 APPENDIX. 

By continuing this investigation further, it has been found that 
the constitutioDj not only of the sun, but nearly, if not all, of the 
heavenly bodies, agree in many particulars with that of this earth. 

It has even been applied to the systems of stars, termed NehvlaVy 
which appear as little clouds of self-luminous matter, of very little 
density, being in a highly gaseous state, and scattered in all 
directions in the remote heavens, the result of which is, that one 
class exhibit spectra similar to the sun and planets, and the other 
a spectrum containing three bright lines : one of hydrogen, one of 
nitrogen, and the third as yet undetermined. This class are termed 
inresolvable, as they always appear, even by the aid of powerful 
telescopes, luminous mists or gases ; the other class are termed 
resolvable, because they appear as immense clusters of stars. 

From these results, the conclusion has been arrived at that the 
sun and other members of the solar system are similar in com- 
position, and this is a great link towards proving that they have all 
been derived from the same source, but in what manner we can at 
present only conjecture. 

Several theories have been put forth accounting for the origin of 
this earth, the chief of which is the "Nebular Theory," by means of 
which Laplace, the great French mathematician, attempted to trace 
the formation and growth of the sidereal bodies from one great 
rotating mass of matter. 

It has been proved by the spectroscope that some of the nebulae 
are gaseous and others stellar ; that is, some are still so hot as to be 
in a state of vapour, but others have so far cooled as to become 
stars. 

The " Nebular Hypothesis " is that, at first, the whole solar 
system existed in a state of vapour only, similar to the gaseous 
nebulas which still exist ; and that all sidereal bodies are continually 
growing, and other bodies forming from the aggregation of nebulous 
matter. 

Laplace, in attempting to trace from physical laws the operation 
of this development, showed that a mass of gaseous or fluid matter, 
when made to rotate rapidly, would spread out in the plane of 
rotation and become a thin disc, becoming wider and thinner as the 
velocity of rotation increased, until the centrifugal force overcomes 
the attraction of cohesion, when whole rings, or parts of the edge, 
would fly ofij and contract by gravitation into masses of a spheroidal 
shape, and still continuing to revolve round the centre from which 
they iaecome detached. In these detached masses, the velocity of 
the outer edge would greatly exceed that of the inner edge, and 



APPENDIX. 171 

tHs excess on one side would give the newly-formed planet a 
rotation on its axis. This process repeated again and again, with 
the same stratum, would form the successive spheroids, each 
revolving in a narrower orbit, until the entire nebula was replaced 
by the system of planetary bodies. 

Again, these planets, as they were formed, might, in their earliest 
stages, throw off their outer edges, or fragments, forming moons or ' 
sateUites revolving round the planet as their centre. 

This is in aU probability the manner in which our earth had its 
origin. An immensely-heated vaporous matter extended for 
hundreds of millions of miles, and, revolving on its axis, the outer 
edge would travel at such a speed that our comprehensions cannot 
grasp. Then, think what its centrifugal force must have been, and 
this would evidently be greatest at the equator. Hence the matter 
would be more likely to fly off from these regions, where it would at 
first foria a belt or ring similar to what stUl exists round the planet 
Saturn. Afterwards, probably breaking its continuity, the particles 
would fly together, forming a planet, which would revolve around 
the original central mass. And as the nebular continued to con- 
dense, planet after planet would be formed, the central mass, or 
what is left of it, remaining an intensely-heated body, consisting of 
a more or less dense nucleus, surrounded by an envelope of vapour 
composed of elements many of which can only exist in that form 
under the influence of extremely great heat. This remaining central 
part of the nebular is the sun, which is, in all probability, stUl 
continuing this process, and must eventually become a solid globe ; 
though, according to calculations made by eminent philosophers, if 
the sun is feeding itself, a diminution of one-thousandth of the sun's 
diameter would produce heat enough to suffice for its entire 
radiation during 21,000 years. 

This theory accounts for many of the phenomena of the solar 
system ; it enables us to see the reason they all revolve round their 
common centre, the sun ; the reason they spin upon their own axis 
in the same direction; and how it is that the remotest planets, 
formed of the most volatile and rapidly-moving matter, are also 
the largest and least dense, while the heaviest and smallest are near 
the centre. 

Our earth itself gives us plenty of evidence tending to confirm 
the theory of its once being in a molten state ; one of the principal 
facts being its spheroidal shape, as it must have been in a fluid state 
to have bulged out at its equatorial regions whilst rotating on its 
axis. Active volcanoes point to the existence, at some unknown 
depth, of enormous masses of matter in an intensely heated state. 



172 APPENDIX. 

and even in a state of fusion as lava. We have also very strong 
evidence on chemical grounds that the earth must have been very 
much hotter than it is now, as many of the compounds of which the 
earth is composed would require very high temperatures for their 
formation. 

We will now bring this paper to a close, having briefly stated the 
most general accepted theory of the origin of this earth. It may 
take years to fully establish this theorj?- and the proof of it ; but 
still we feel certain it is only a matter of time. 



173 

SYLLABUS OF PHYSIOGRAPHY ISSUED BY THE 
SCIENCE AND ART DEPARTMENT. 

FIRST STAGE, OR ELEMENTARY COURSE. 

2%e candidate will be expected to have a knowledge of ordinary Descriptive and 
Physical Geography— so far as required by the Fifth and Sixth Standards of the 
New Code, and of the specific special subjects of secular instrvxtion— Principles of 
Mechanics, and Physical Geography. 

Questions r/iay be set in these subjects : — 

The parts played by gravitation, cohesion, and chemical affinity in produc- 
ing chemical and physical difierences in matter. 

Elementary ideas of the various conditions of matter as regards energy, 
embracing heated states and electric and magnetic states. 

Elementary notions of chemical action. The formation of binary com- 
pounds. 

Breaking up of compound matter into simpler forms. The chemical 
elements. 

Water. — Its composition and several states. 

Chemical and Physical Character of the Crust of the Earth. — Eocks, 
stratified and unstratified. Inorganic Materials (the more frequent simple 
minerals formed of them) : Granite, volcanic products (ancient and modem), 
sedimentary rocks, conglooierate sandstone, shale : limestone gneiss, slat«, 
marble, sand, mud, and surface soil. Materials partly produced by organisms : 
Coal, peat, chalk, coral, and limestone. Bodies of which these are compounds. 
The chemical elements of which the crust is chiefly composed. Observations 
indicating an increased temperature in the interior of the earth. Volcanic 
Phenomena, and distribution of volcanoes. Earthquakes and slow upheavals 
and subsidences of the earth's crust. 

The Sea.— Salts dissolved in sea water. Depth and form of sea bottom. 
Remarkable inequalities. The chief currents. Distribution of temperature 
and density. Phenomena of Arctic and antarctic i-cgions, floes, pack ice, 
icebergs, &c. Action of the sea on the earth's crust. Influence of the sea 
on the distribution of climate. 

The Atmosphere.— Height and composition. Atmospheric pressure. Uso 
of the barometer. Distribution of temperature, horizontal and vei-tical. Use 
of the thermometer. Evaporation and condensation. Aqueous vapour, 
rainfall, ice, snow. Region of extreme dryness and of great rainfalls. The 
prevailing air cun-ents. Cyclones. General conditions of climate. 

Action of rain, springs, rivers, and glaciers upon the earth's crust. 

General ideas of the changes which the earth's surface has undergone in the 
past, and of evidence as to succession of various forms of life. 

Elementary notions as to the effects of terrestrial electricity and 
magnetism ; thunderstorms ; avurora ; the mariner's compass. 



EXAMINATION PAPERS. 



PHYSIOGRAPHY. (1877). 

Examiners.— J. Norman Lockyer, Esq., F.R.S., and John W. Judd, Esq. 

first stage, or elementary examination. 

Instructions, 

You are permitted to attempt only eight questions. 

The first foiu: questions must be attempted by you, and you are then at 

liberty to select four others from among the remaining questions on the paper. 

The value attached to each question is indicated by the numbers in brackets. 



174 EXAMINATION PAPERS. 

51. What are deltas? How are deltas formed? Name six of the largest 
deltas in the world. [See 89.] (15) 

52. Why does rain fall in such great abundance in the west of Ireland ? 
What is meaiat by the statement that the mean annual rainfall of a place is 
70 inches ? What becomes of the water which faUs upon the earth ia the form 
of rain? [See 111 and 87— 90]. (15) 

53. What is meant by the snow-hne? Why is the snow-Hne sometimes 
higher on one side of a mountain chain than on the other? Why do glaciers 
descend below the snow-line? [See 112, 75, 112]. (15) 

54. What is a volcano? Name the active volcanoes of Europe, and state in 
what parts of the same continent extinct volcanoes occur. [See 51—54]. (15) 

55. State, in the order of their relative abundance, the eight chemical 
elements which enter most largely into the composition of rocks. [See 44]. (10) 

56. What is the difference in composition between peat and coal ? By what 
changes would the former pass into the latter? [See page 40]. (10) 

57. Of what materials are clay, shale, and slate chiefly composed, and in 
what respects do these rocks differ from one another ? [See 47]. (10) 

58. What is the principal work performed by rivers in modifying the 
features of the earth's surface? Ex i lain the mode of origin of the winding 
curves in which rivers so frequently flow. [See 88, 89, and 114]. (10) 

59. Draw a sketch map of the Atlantic Ocean, and indicate upon it the 
courses of the chief of the great currents. [See Maps and 35]. (10) 

60. What are the differences between continental and insular climates, and 
how are these differences caused ? [See 116]. (10) 

61. In what direction does a magnetic needle in this country point, and 
why does it not everywhere assume a due north and south direction? [See 
83, 34, and 146]. (10) 

62. Why are coral reefs limited to certain restricted areas of the earth's 
surface? (10) 

SECOND STAGE OR ADVANCED EXAMINATION. 

Instructions. 
You are permitted to attempt only six of the following questions, and the 
three which stand first on the paper m\ist be included among these. 
The value attached to each question is indicated by the number in brackets. 

71. A steamer crosses the Pacific from Vancouver Island to Otago. State 
the nature and direction of the great permanent air-currents which she may 
be expected to encounter at different points during the voyage, and explain 
the causes to which each is due. [See Maps, and 104— 107. J (18) 

72. Explain the procession of the equinoxes. [See 65, latter part.] (19) 

73. How has the chemical composition of the solar atmosphere been deter- 
mined, and how can we measure the velocity with which the various vapours 
move in that atmosphere ? [See 139]. (18) 

74. State the various grounds on which it is inferred that a high temperature 
exists in the eai'th's interior. [See 51 — 52]. (15) 

75. Explain the origin of grotmd-ice, pack-ice, and icebergs. [See 115]. (15) 

76. Describe the several methods by which beds of limestone are now being 
formed upon the earth's surface. [See 47J. (15) 

77. What conclusions concerning the origin of the physical features of the 
moon have been deduced from its telescopic appearance? [See 60]. (15) 

78. How has the size of the earth been determined ? [See 145]. (15) 

79. What are the three elements to be observed before the state of the 
earth's magnetism at any place and time can be determined ? [See 34], (15) 

■•• HONOURS EXAMINATIONS, 

Instructions. 
You ape permitted to attempt only four questions, but these may be 
' Belect'ed from any part of the paper. 
.: The value attached to each question is the same. 



EXAMINATION PAPERS. 175 

91. State the various methods by which the density of the earth has been 
determined. What are the results wliich have been arrived at? Compare 
the density of the earth with that of the other planets. [See 62, and table, 142.] 

92. What are the different theories which have been put forward in 
explanation of the origin of volcanic cones and craters ? State the arguments 
for and against each of these theories. [See 53, <fec.] 

83. Explain the nature and probable mode of origin of the several different 
kinds of deposits now being formed in the deepest explored portions of the 



94. State the chief differences which have been observed in the stella spectra, 
and the conclusions which may be drawn from these differences. [See 140.] 

95. Describe the instruments in a self-recording magnetic observatory. [See 
146.] 

86. Give an account of the results which have been obtained by recent 
researches in connection with one of the following subjects : — 
(a) The constitution of the sun. [See 139.] 
(6) The origin of the ocean currents. [See 85.] 

(c) The distribution of temperature on the earth's surface during former 
periods of its history. 

(d) The nature of its liquids occupying minute cavities in the crystals of 
rocks. -^^ 

SUBJECT XXIII.— PHYSIOGRAPHY. (1878). 
Examiners— Prof. John W. Judd, F.R.S., and J. Norman Lockyer, Esq., F.R.S. 

FIRST STAGS OR ELEMENT.4RY EXAMINATION. 

You are permitted to attempt only eight questions. The first four questions 
must be attempted by you, and you are then at liberty to select four others 
from among the remaining questions on the paper. 

51. The river Rhone enters the Lake of Geneva as a muddy stream, and 
leaves it as a perfectly clear one. State the source whence the sediment car- 
ried by the river is derived, and what becomes of it. Explain the changes 
which are being produced in the physical features of the country by the 
removal and re-deposition of the material carried by the river. [See 89.1 (15) 

52. What is a "bore"? How are bores produced? Name three rivera 
which exhibit this phenomenon. [See 84, latter part.] (15) 

53. How is dew formed? State the conditions of atmosphere which inter- 
fere with the formation of dew ; and explain how the deposition of dew is 
checked by these conditions. [See 109.] (15) 

54. In what respects do a volcano and a geyser resemble one another, and 
in what respects do they differ ? Name the principal districts on the globe in 
which geysers are found. [See 51—64.] (15) 

55. Name four of the most common minerals which enter into the compo- 
sition of the earth's crust, and state the elements of which each is composed. 
[See 44.] (10) 

56. Describe the minute structure of a piece of chalk, and show how, by 
simple experiments, the two oxides of which it is composed may be respec- 
tively isolated. [See 47, 21, 43—44.] (10) 

V. 57. State the different methods by which the heights of mountains can be 
determined. [See 98— 45.] (10)' 

58. Draw a sketch-map of Africa, and indicate upon it the positions of ita 
great lakes, and the courses of its principal rivers. [See maps.] (10) 

59. What are isobars? State the causes to which.their continual changes in 
position are due. [See 116.] (10) 

60. Describe the mode of origin of icebergs. [See 115.] (10) 

61. What are the magnetic poles, and what do you know about their geo- 
graphical position ? [See 32—33.] (10) 

62. In what parts of the globe are elephants now found ? Is there any 
evidence that they once lived in other areas ? and, if so, state the nature ol 
that evidence. [See 121—57, Eocene and Miocene period.] (10) 



176 EXAMINATION PAPERS, 

SECOND STAGE OR ADVANCED EXAMINATION. 

You are permitted to attempt only six of the following questions, and the 
three which stand first upon the paper must be included among these. 

71. Describe the principal methods which have been devised for determin- 
ing the longitude of a place. [See 143.] (18) 

72. State the general facts at present known concerning the temperature 
of the waters of the ocean. [See 85 for each ocean.] (19) 

73. What are the nature and composition of the chief materials ejected from 
•volcanic vents? [See 53 and 49.] (18) 

74. Explain the principle on which the sending of storm-warnings from 
America is based, and state the causes which may prevent these predictions 
from being fulfilled. (15) 

75. How has it been proved that the earth is not a perfect sphere? 
[See 145. J (15) 

76. State what you know about nutation. [See 65.] . (15) 

77. What is an " arc of parallel," and "an arc of meridian?" Give examples 
of both. [See 145.] (15) 

78. What are earth currents ? [See 26.] (15) 
79.. Compare the chemical constitution of the crust of the earth with that 

of the sun's atmosphere, comets, and nebulae. [See 44-46 and 139-141.] (15) 

HONOURS EXAMINATION. 

You are permitted to attempt only four questions, but these may be selected 
from any part of the paper. 

91. Give an account of the apparatus by means of which observations have 
■been made in the deeper parts of the ocean ; and describe the general form 
of the bed of the Atlantic Ocean. [See 85.] 

92. Explain the methods by which the depth of the shock producing an 
earthquake-wave can be determined. 

93. State the chief arguments that have been adduced against the hypothesis 
that the earth consists of a solid shell with a liquid interior. [See 52.] 

94. Describe the phenomena presented by aurorse, and state what you 
know concerning the hypotheses which have been put forward to account for 
their production. [See 36 and 29.] 

95. State the facts which have led to the view that meteorological changes, 
and changes in terrestrial magnetism, are connected with one another. [See 
29-36.] 

96. Give an account of the results which have been obtained by recent 
researches in connection with one of the following subjects : — 

(a) The density of the earth. [See 62.] 

(6) Double and multiple spectra of the same elementary body. [See 135 
and 139.] 

(c) The measurement of the sun's distance. [See 129.] 

(d) The cause of the movement of bubbles in the liquids enclosed in minute 
cavities of the crystals of rocks. 

(e) The existence of man during or before the glacial epoch. 

The first numbers in brackets are the paragraphs where the information may bf 
found. The other number i$ its value at the examination. 



EXAMINATION PAPERS. 177 

PHYSIOGRAPHY. (1879). 

FIRST STAGE OR ELEMENTARY EXAMIKATION. 

Instructions. 

You are permitted to attempt only eight questions. The first three 
questions must be attempted by you, and you are then at liberty to select 
five others from among the remaining questions on the paper. 

The value attached to each question is indicated by the numbers in 
brackets. 

1. What is the number of known chemical elements? Name the six 
elements which occur in greatest abundance in the crust of the earth. State 
the condition in which the metallic elements generally exist in that crust. 
[See 39 and 44.] (15) 

2. When water is left standing in a vessel out of doors, it gradually 
disappears. State what becomes of the water, and under what conditions of 
atmosphere it will disappear most rapidly. [See 108 and 109.] (15) 

3. State what rock-constituents are carried by rivers to the sea in suspension 
and solution respectively ; and describe what becomes of those materials 
when they reach the sea. [See 87-89.] (15) 

4. How do you explain the fact that fringing coral reefs generally occur in 
volcanic areas, and atolls, encircling-reefs and barrier-reefs, in non- volcanic 
areas ? [See 56.] (11) 

5. Describe the principle of the construction of the mercurial barometer. 
[See 96.] (11) 

6. What are moraines ? Name the different kinds and describe the manner 
in which they are formed. [See 122.] (11) 

7. Draw a sketch map of the Mediterranean Sea, showing the positions of 
the chief islands. [See map.] (11) 

8. Name the minerals which occur in a piece of granite, and describe their 
chemical composition. [See 44.] (11) 

9. What is the chemical composition of a piece of common coal, and how 
does it differ in composition from peat on the one hand and anthracite on the 
other? [See47-<2).] (11) 

10. What is the cause of the noise heard during thunderstorms? [See 30.] (11) 

11. Describe some of the forms foimd in snowflakes, and explain their 
origin. [See 112.] (11) 

12. What evidence have we that lions and tigers once lived in this country? 
[See 57.] (11) 

SECOND STAGE OR ADVANCED EXAMINATION. 

Instructions. 

You are permitted to attempt only six of the following questions, and the 
three which stand first upon the paper must be included among these. 

The value attached to each question is indicated by the numbers in 
brackets. 

1. Draw the earth, as seen from the sun, at the two solstices and equinoxes, 
showing the direction of its axis and the positions of the north and south 
poles. (IS) 

2. Describe the trade winds, and state the causes to which they are due. 
[104 and 103.] (IS) 

3. State the different kinds of evidence from which it is inferred that 
certain parts of the earth are being upheaved, and others are subsiding. 
rSee 56]. (19) 



178 EXAMINATION PAPERS. 

4. Explain the cause of the difference between the climates of London and 
Moscow. [See 45, latter part, and 116.] (15) 

5. Name the several gases of which the atmosphere is composed, the pro- 
portions in which they are present, and the manner in which they are united 
with one another. [See 92.] (15) 

6. What proofs have we of the existence of a high temperatiu-e within the 
earth? [See 51.] (15) 

7. Describe a transit-circle and its uses. (15) 

8. How does a dipping needle behave at the magnetic poles, and why? 
[See 32-34.] (15) 

9. What terrestial phenomena seem to be connected -with, the number of 
spots seen on the sun at different times ? [See 26, 35, 58, and 138.] (15) 

HONOURS EXAMINATIOK. 

Instructions. 

You are permitted to attempt only four questions, but these may be selected 
from any part of the paper. 
The value attached to each question is the same. 

1. Explain the construction of any forms of seismometers or seismographs 
with which you are acquainted. 

2. Mention the several theories which have been advanced to account for 
the existence of the great rock-basins occupied by lakes ; and state the 
argtunents for and against each of these theories. 

3. Describe the composition of the different classes of meteorites and com- 
pare it with that of the earth's crust. 

4. State what you know about the spectrum of Sirius and Uranus res- 
pectively ; and the conclusions which have been drawn from the observations. 

5. How has the connection between luminous meteors and comets been 
established, and what is the nature of the connections ? 

6. Give an account of the results which have been obtained by recent 
researches in connection with one of the following subjects : — 

faj The distance of the sun as determined by observations ot Mars at 
opposition. 

(bj The spectrum of oxygen. 

fc) The nature of volcanic products dtu-ing the older Palseozoic periods. 

^dj The existence of great continental "ice-sheets." 



PHYSIOGRAPHY. (1880.) 

riRST STAGE OR ELEMENTARY EXAMINATION. 

1. Name the binary compounds which are united to form a piece of lime- 
stone ? State how these may be separated from one another, and describe 
the characters presented by each of them ? What elements are present in 
these binary compounds, and what is the general character of each of these 
elements ? 

Limestone is calcic carbonate. TJiat is, it consists of the binary/ compounds — 
Calcite and carbonic acid. 

By burning the limestone the carbonic acid is expelled and pure lime, or quick- 
lime, is obtained. 

Carbonic acid is colourless gas, having a slight acid taste and smell. It is very 
poisonous. 



EXAMINATION PAPERS. 179 

Cdlcite, or pure lime, is a white, opaque, inodorous, acrid alkaline and infusible 
substance. If it be sprinkled with water it heats, swells, cracks, becomes 
powdery, and forms "hydrate of lime," ov "slacked lime." 

Calcite is formed by the union of the two elements, calcium and oxygen : and 
carbonic acid, by the union of carbon and oxygen. Hence the elem,ents 
are calcium, carbon, and oxygen. 

"Oxygen" is a gas which is devoid oj colour, taste or smell. It is transparent 
and invisible. It possesses the mechanical properties of common air. It is 
capable of being respired, and a given volurtie of it will siipport life much 
longer than an equal bulk of common air. It possesses great pozoer of com- 
bination with other elementary bodies, there being scarcely one which is not 
known to combine dth&r by direct union or in direct chemical action. The 
most remarkable property of oxygen gas is the facility and splendour with 
which bodies when previously ignited burn in it. Substances which do not 
undergo combustion in the air, will readily do so and with great brilliancy 
in oxygern, gas. Thus, iron, for example, bums very readily in it when, 
previously made red hot. 

•' Csilcium" is a yellowish white metal, which can he rolled into sheets and Tiam- 
mered leaves, and is intermediate between lead and gold in Tiardness. 

"Carbon" is a non-metallic solid element. The commonest form in which we 
find this siibstance is as charcoal — black charcoal. It is also very comraon 
in the form of black-lead, of which drawing pencils are made. Other names 
for this form of carbon are pVambago and graphite. Carbon also occurs 
in nature as diamond, being very pure carbon crystallised. 

Carbon exists in combination with other elements as gases, in all animal and 
vegetable substances. The coal we bum contains large quantities of this 
element together with hydrogen. 

2. Describe the construction and use of a thermometer, and explain the 
methods by which thermometers are graduated, [See 101.] (15) 

3. Why is the south-west wind in this coimtry usually accompanied by rain, 
while the east wind brings dry weather ? 

TTie "South-west wind" blows across the Atlantic, coming from "warm, regions" 
so that it takes up a great amount of moisture, which it precipitates when, 
it reoxhes cooler regions. The " East-wind," on the other hand, comes to us 
across the vast plains of Northern Germany. In the latter part of the 
spring those plains are very cold, and tTierefore the winds are found to 
he very severe. They do not bring rain because their track has been over a 
vast area of land. 

6. What are fiords ? and how do you suppose them to have been formed ? 
Narrow arms or choMnels of the sea, or the widening of a river into arms of the. 

sea. Numerous fiords are to be found on the coast of Norway, 
Thete fiords have been fo-nned by the action of the sea upon the coast. For 
instance, the country of Norway is raised considerably above the level of the 
sea. The coast, therefore, o_ffers special resistance to the waters as they rush 
inwards. They in their turn carry on a loork of disintegration in several 
ways, viz., by the force of the brea,kers (S6J ; by its action of decomposing 
rocks (Ai); by frost, c&c. (UU); so that the softer rocks have to give way to 
the sea, while the harder still contend, against it. 

7. Describe the phenomena called roches rnoutonnees, and explain how they 

are formed ? (11) 

"Roches rnoutonnees," (Fr. roche, a rock and moutonnee, sheep-like) is the name 
given to rocks which possess a peculiar rounded a,ppearance, some of which 
froiii their shape have been likened to the backs oj sheep. 



180 EXAMINATION PAPERS. 

They are formed through the action of glaciers, &c., on the rocks, which caused 
them to become grooved and polished, though the ice does not plane the 
surface evenly, but merely removes the jagged and projecting points. 

8. Draw a sketch map of Hindostan, showing the position of its great 
mountain ranges and rivers. (N.B. -Names must be given.) [See Maps, &c,] 

(11) 

9. Name six of the minerals which occur most commonly in igneous rocks 
and describe their composition. [See 49-50 and 44.] (11) 

10. How is kaolin derived from granite? Describe the several stages 
of the process. [See 44.] (11) 

11. What is the cause of the interval which elapses between a flash of 
lightning and its accompanyiug thunderclap? If this interval, in any 
particular case, were found to be 11 seconds, what inference would you 
draw from the fact ? (11) 

It is the difference in time it takes the light and sound to travel from the place 
where it occurred to the observer, as light travels at the rate of 186,000 
miles a second, and sound at 1,090 feet per sfcond. Hence if the interval 
between the Hash and the thunder-clap were 11 seconds, the distance from 
me to the place where the clap originated would be 1,090x11=11,990 feet, 
or about ^j miles, 

12. What is meant by the statement that certain forms of life have become 
extinct ? State some of the causes which have brought about the extinction of 
animals, and name any animals which have become extinct since the 
appearance of man. [See 57.] (11) 



SECOND STAGE OR ADVAITCED EXAMINATION. 

1. State what you know about the apparent movements of the stars and 
the causes which give rise to them. [See lb4 and 135.] (23) 

2. Explain the methods by which the quantity of material cai-ried down by 
rivers in suspension and solution respectively, can be determined. How may 
this he made to guage the rate of subaerial denudation within the river 
iMin? (23) 

Firstly, the average quantity of water brought down by the river in a given time 
must be found. Then one unit of the quantity must be examined, and the 
quantity of matter found to have bten deposited at the bottom of the vessel 
added to the quantity of matter held in solution and set at liberty by 
chemical means. This result multiplied by the number of imits in the 
quantity brought down in the given time, gives the total quantity in that 
time. Thus, for example, it has been calculated that the average quantity 
of water that flowed in the river Thames through Kingston, in wet and fine 
weather, is 1,250,000,000 gallons in 24 hours. A gallon of the watei- was 
examined and found to contain 19 grains weight of mineral, principally 
carbonate of lime, which was held in solution by the water, besides the 
sediment. Hence, on a fine day, when hardly any mud, is being carried doicn 
the Thames, past Kingston, no less than 3,364,286 lb. weight of invisible 
matter is hurrying along to the ocean. 

To guage the rate of subaerial denudation, we must calculate the quantity of 
rockwhich must have been woo'n away to yield the quanf^*" of mineral found. 
Thus a to'n, of carbonate of lime makes up about a cubic yard, of solid, 
rock, and therefore 3,364,286 lb., or 1,502 tons, are equal to 1,502 cubic 
yards, which is removed every day, or 548,230 cubic yards per year. 
[SeeSS.'' 



EXAMINATION PAPERS. 181 

3. Describe the monsoons; stating the periods at which they blow, the 
countries in which they are felt, and the causes to which they are due. [See 
105 and 104.] (18) 

4. Explain the action of plants and animals upon the constituents of the 
atmosphere. [See 92.] (18) 

5. Describe the principle of the construction of the aneroid barometer, 
[See 96.] (18) 

6. What are the views at present concerning the nature of Saturn's rings, 
and what are the facts on which these views are based ? [See 130-131.] (18) 

7. Explain the terms " dispersion " and "minimum-deviation," as applied 
to a ray of light. [See 138, 139, and 99.] (18) 

8. How is the intensity of terrestial magnetism at any place of observation 
determined 1 [See 33, 34, and 146.] (18) 

HONOURS EXAMINATIOSr. 

1. Explain the several theories which have been proposed to account for 
the spadmodic action of geysers, and state the arguments for and against 
each of these theories. [See 51-54.] 

Another theory put forward is 

The action of water upon vast beds of pjrrites. 

In geyser regions extensive beds of sul;phur and 'pyrites ore to he found, Deeom- 
position oj the latter is readily produced by the agency of water and air, 
and in the process of decomposition great quantities of heat are evolved. 
The heat produced by this action is sufficient to raise an additional quantity 
of water in the form of steam, which makes its way to the surface, and is 
there emitted through the different clefts in the roch. 

The character of the soil and rock in the geyser districts, both of Iceland and 
North America, strengthens this theory, and so do the other surroundings. 
In all cases there is free access of water— free sulphur is widely dispersed, and 
the steam-jets are invariably accompanied by large quantities of sulphuretted 
hydrogen. 

2. Explain by the aid of a sketch-map the course of the tidal wave around 
the British Islands. [See map.] 

3. State what you know about the spectrum of a Lyrce and the sun res- 
pectively, and the conclusions which have been drawn from the observations. 

4. State the probable climatic conditions of Mars and Jupiter. [See 130.] 

5. Give an account of the results which have been obtained by recent 
researches in connection with one of the following subjects : — 

(a) The nature of the sun's corona. 

(b) The microscopic character of the sedimentary rocks. 



PHYSIOGRAPHY. (1831.) 

FIRST STAGES OR ELEMENTARY EXAMINATION, 

1. What chemical elements are present in water ? How can water bo 
separated into its elements, and how can these elements be made to re-unite 
to form water ? [See 45.] (15) 

Water can he separated into its elements by analysis. This is done by a 
decomposing apparatus, consisting of a trough, two tubes, two pieces of 
platinum-ioil, and connected with a galvanic battery. The trough is half 
ailed with water containing a little oil of vitriol. The two tubes are filled 
with water and inverted, each over a piece of platinum-foil, which is 



182 EXAMINATION PAPERS. 

attached to a copper wire. The wires pass through the hottovii of the trough 
to the outside, where they are connected with the wires of a galvanic battery. 
By the action of the battery oxygen is given off in the tube joined to the 
copper or 'positive end, and hydrogen in the one attached to the zinc or 
negative end of the battery. It will be noticed that the hydrogen tube is 
filled in about half the time that the oxygen tube is filled, clearly proving 
that the water contains " tico " volumes of hydrogen to " one " of oxygen 

Fill a soda-water bottle two-thirds full of hydrogen and one-third of oxygen, 
then " wrap a towel well round it," and apply a light, the gases toill explode 
with a loud report, forming two measures of watery vapour. 

2. Why does ice usually form on tlie surface of water and under wliat 
circumstances is it occasionally formed at the bottom of a piece of water ? 
[See 45 and 112.] (15) 

3. On what grounds is it helieyed that a high temperature exists in the 
deeper part of the earth's crust? [See 51 and 52.] (15) 

4. Explain the fact that no dew is found upon the ground after a cloudy 
or windy night. [See 109 and 108.] (11) 

5 Describe a raised-beach, and state what inference you would draw from 
its existence. [See 53]. (11) 

6. Explain the nature and cause of the difference between continental and 
insular climates. [See 45, latter part, and 116.] (11) 

7. Draw a sketch map of Africa, marking on it the positions of the cMef 
rivers and lakes. — (N.B. Names must be given.) [See Maps.] (11) 

8. State the causes which may give rise to an excessive rainfall in a 
district, illustrating your remarks by examples. [See lll.[ (11) 

9. Explain the formation of coal. [See 47 (2)] (11) 

10. In what respect do slate and shale respectively differ from clay. [See 
47 (1)] (11) 

11. What is meant by the snow-line, and on what conditions does the 
height of the snow-line on different mountain chains depend? [See 
112.] (11) 

12. Explain what is meant by the " geographical range " of a species of 
animal or plant. [See 117, &c.] 

SECOND OR ADVANCED STAGE. 

1. Describe the changes which wiU take place in the volume of a pound of 
water as its temperature is raised from 0°P. to 300°F. 

At 0°F. it is ice, and occupies roughly speaking about eleven-tenths the volume it 
will have at STF. when in a state of water. From S2°F. upwards it 
decreases in volume till reaching 89" F. when it attains its maximum density — 
thfxt is, its minimum volume. As the temper atureriseahigher, the water again 
expands. The co-efficient of expansion increasing as the temperature rises, 
until it reaches 212°, when the volume has increased to I'OkS volumes, and 
at 300° if the pressure is so great as to prevent it becoming steam it will 
occupy Vl volumes, biit at the ordinary pressure of the atrnos'phere it would 
become steam at 212°, and occupy about 1,800 times the volume it d,id at S9°F. 

2. State what you know about Kepler's laws. [See 58.] (23) 

3. What is the cause of the low temperature which prevails at the bottom 
of the deep oceans ? [See 85.] (IS) 

4. What are hygrometers ? Explain the construction and mode of use of 
Eome form of hygrometer. 

Hygrometers are instruments used for tJie purpose of estimating the amount of 
moisture in the atmosphere at any given time. The principle ujyon ^ohich 
vwst hygrometers are constructed, is this: — The temperature at which the 



EXAMINATION PAPERS. 183 

• vapour in the air has its maximum tension is determined, that is, at what 
temperature moisture just begins to separate from the air, which is called 
the dew-point. When this point is known it is not difficult to calculate 
approximately the absolute quantity/ of moisture in any bulk of air. 

Daniel's hygrometer consists of a closed glass tube, terminating at both extremities 
in bulbs, and bent twice at right angles. One bulb is artificially blackened 
so that any moisture upon it can be readAly seen; this bulb contains some 
ether and also a thermometer partly immersed in the ether. The other bulb 
is empty, and is surrounded with muslin. The whole rests upon a stand 
upon which there is another thermometer that indicates the temperature of 
the air. Jj some eth^r is poured on the muslin, the temperature of the bulb 
falls, and the ether vapour within it, %ohich is derived from the liquid in 
the other bulb, will become liquid. The space which is thus rendered vacant 
will instantly be filled with more vapour from the liquid. The evaporation 
going on in this bulb will lower the temperature of the bulb, and this process 
can be carried on until it (the bulb) is cold enough to cause dew to be 
deposited upon it from the air surrounding; the thermometer in the ether 
will then indicate the dew-point. If some ice is put into a perfectly dry 
tumbler, the outside of the tumbler will soon become wet from the deposition 
of dew, just as the bulb containing the ether becomes wet. 

5. Describe the characteristic features of the different kinds of volcanic 
cones, known as scoria-cones, tufa-cones, lava-cones, and compound-cones. 
[See 53-56.] (18) 

6. How are the colours produced in the rainbow? [See 100 and 99.] (18) 

7. Explain the equation of time. (18) 

8. "What are the principal phenomena observed in a total eclipse of the 
sun? [See 131.] (18) 

HONOURS EXAMINXTIOK. 

1. State and discuss the various objections which have been raised against 
the hypothesis that the earth consists of a solid outer shell with a fluid 
nucleus. [See 52.] 

2. In what respects does Globigerina-ooze resemble chalk, and in what 
respect does it differ from that rock? 

3. What are the methods generally adopted in measuring a base-line for a 
geodelical survey ? 

4. State what is known about the satellites of Mars. 

5. Give an accouot of the results which have been obtained by recent 
researches in connection with one of the following subjects : — 

(a) The artificial formation of crystallised minerals. 
(bj The spectra of the fixed stars. [See 137 and 141.] 



184 EXAMINATION PAPEES. 

SET AT THE CHRISTMAS EXAMINATIONS FOR 

TEACHERS. 

SUBJECT XXIII. -PHYSIOGRAPHY. (Christmas, 1S78.) 

Examiners— Prof. John W. Judd, F.R.S., and J. Norman Lockyer, Esq., F.R.S. 

General Instructions. 

If the rules are not attended to, the paper will be cancelled. 

Put the number of the question before your answer. 

You are to confine your answers strictly to the questions proposed. 

Your name is not given to the Examiners, and you are forbidden to wi-ite 
to them about your answers. 

You are permitted to attempt only six of the following questions, and the 
three which stand first upon the paper must be included among these. 

Three hours allowed for this paper. 

1. State how you would explain to a class the mode of the formation of 
dew, and describe any illustrations you would employ in order to make the 
matter clear to the minds of your scholai's. [See 109.] (18) 

2. Explain by the aid of a diagram the internal structure of volcanic cinder 
cones, and state the causes to which that structure is due. [See 53. &c.] (18) 

3. Imagine that you are explaining to a class the cause of the seasons. 
"Write down what you would say, and give the diagrams j-ou would make. 
[See 64 and 65.] " (19) 

4. In what portions of the globe are rainless areas situated? State the 
causes of the drjoiess of climate in each case. [See 111 and 112, &c.] (15) 

5. Explain the agencies by which a piece of granite is disintegrated, and 
enumerate the products of this disintegrating action. [See 44. ] (16) 

6. What are the principal salts dissolved in sea water? Explain what 
becomes of the various materials carried in a state of solution by rivers to 
the ocean. [See S3.] (15) 

7. State how the distance of the moon from the earth has been determined. 
[See 129.] (15) 

8. Describe the construction and mode of use of the spectroscope. State 
what you know about the spectrum of sodium, of chlorine, and of the sun. 
[See 138.] (15) 

9. What is a dip-circle or dipping needle ? How is it used, and what has it 
taught us? [See 33.] (15) 



PHYSIOGRAPHY. (Christmas, 1879.) 
General Instructions. — See 'preceding Paper. 

1. Give notes for a lesson to a senior class " On the evidence which coral- 
reefs afford of great movements taking place in portions of the earth's crust." 
[See 56-57.] (15) 

2. Enumerate the varieties of ice-masses which are found in the Arctic and 
Antarctic regions, and explain the mode of origin of each. [See 115-113- 
114, (fee] (15) 

3. Write down what you would say, and give the diagrams you would make, 
in explaining the phases of the moon. [See 60.] (15) 

4. Describe the phenomena presented by the land and sea breezes, and state 
the causes to which they are due. [See 105.] (12) 



EXAMINATION PAPERS. 185 

5. State "what you know about the composition of white light and show 
(1) how this may be studied by simple experiments and (2) its bearing upou 
the composition of stars. [See 138-141.] (12) 

6. Describe the construction of a mercurial barometer, and explain its mode 
of action. "Why is mercury the flmd usually employed for barometric pur- 
poses? [See 96.] (15) 

7. Does the mariner's compass always point true north and south ? If not, 
why not ; and where is the greatest variation at the present time ? 
[See 33-34.] (15) 

8. State what gases are given off during the conversion of vegetable tissue 
into peat, coal, and anthracite ; and describe the differences in composition 
of these four substances. [See 47 (').] ^20) 

9. State how the distance of the earth from the sun has been determined by 
observation of Mars at opposition. [See 129.] (20) 



iPHYSIOGRAPHY. (Christmas 1880). 
General Instructions. — See Pa;ger for 1878. 

1. Describe a series of simple experiments, not involving the use of any 
costly apparatus, by means of which you would illustrate to a class of children 
the properties and composition of the atmosphere. (25) 

2. Write down what you would say and give the diagrams you would 
make in explaining to a class the causes of the variation of the length of the 
day in the different seasons of the year. [See 64.] (25) 

3. What are the chief facts known concerning the nature of the movement 
of glaciers, and the rate at which this movement takes place? Describe the 
observations by which these facts have been discovered. [See 113.] (20) 

4. What is the equation of time and what is mean time ? (20) 

5. Give a short account of the principle kinds of organisms whose remains 
go to build up limestone-rocks. [See 47 (2) &c.] (15) 

6. What facts relating to terrestrial magnetism are given in a magnetic 
chart of the earth's smrface ? (15) 

7. Explain the nature of earthquake and describe the chief phenomena 
which accompany them. [See 55]. (15) 

8. What has the spectroscope taught us concerning the chemical and physical 
constitution of the atmosphere of the sun? [See 138.] (15) 



186 



INDEX. 



PAGE 
Acids 29, 31 

Actinic Kays 139, 151 

Aerolites -. 146 

Age of the Earth 58 

Age of Fishes 56 

Age of ReptUes 57 

Alabaster 42 

Alkali 30,31,37 

Alum 27 

Aluminium 28, 30, 33, 38 

Ammonites 56, 57 

Animals 132, 134, 135 

Annual Motion 65 

Antarctic Regions 123 

Antarctic Ocean 71, 93 

Anthracite 40 

Appendix 139 

Apsides 66, 67 

Aqueous Rocks , 36 

Aqueous Action 55 

Arctic Expedition 124 

Arctic Ocean 71, 93 

Arctic Regions 123 

Climateof 124 

Arcturus 148 

Arenaceous Rocks 36 

Argillaceous Rocks 87 

Artesian Wells 47 

Ashes 45, 48, 49 

Asteroids 59, 141 

Asterolepis 55 

Astronomical Geography .... 59, 138 

Atlantic Ocean 71, 89, 90 

Atmosphere ..20, 21, 33, 63, 104, 

108. 110, 115, 143, 145 

Composition of 104 

Pressure ..,.-.,. 105 

Height -. 105 

Density. 105 

Temperature 106 

Atolls 53, 54 

Atoms 12, 27,28 

Attraction 12, 13, 15 

Attractive Energy 14, 19 

Auglte 32, 44 



PAGE 

Auroras 20, 25 

Avalanches 121 

Axis of the Earth 65, 66, 125 

Axis of the Planets 143 

Barometer 106, 107 

Barrier-reefs 53, 54 

Basalt .31 

Bases 29 

Beaches Raised JJ* 

Belemnites 56, 57 

Binary Compounds 17, 29 

Birds 132,133 

Bores 89, 114 

Boulders 123 

Breakers 87, 93 

Breccia 36 

Brightness of the Sun 62 

Cainozoic Period 65 

Canons , 84 

Carbonic Acid 31 

Carboniferous System 55, 56 

Chalk 38, 39, 55 

Chemical Action 26 

Affinity 17 

Elements 26,27 

Rays 139,151 

Chemically-formed Rocks 41 

Chert 39 

Chromosphere 62, 152 

Climate 124, 125, 126, 128 

Clouds 116 

Cloud Belts 143, 144 

Coal 39,40, 124, 125 

Coast-lLnes 73 

Cohesion 15, 17, 93,94 

Comets 59, 146 

Compass 23, 25 

Compounds (Binary) 17, 26, 2§ 

Compounds (Broken up) 30, 31 

Condensation 115 

Configuration of Land 72 

Conglomerate 37 

Conical Projection 161 



INDEX. 



187 



PAGE 

Coial 39 

Islands 72 

Keefs 53,54 

Corona 62 

Cretaceous System 55 

Crust of the Earth ... .27, 30, 33, 

35, 93, 122 

Cryptogams 128 

Currents 89 

Cyclones 114 

Day and Night 65 

Declination 23, 24, 25 

Definitions 67, 68, 69, 70 

Deltas 97 

Density of Earth.. „ 47, 64 

Planets 64,142 

Oceans 84 

Depth of Ocean 89, 91, 92, 93 

Dew 115 

Distance of Heavenly Bodies .... 142 

Distribution of Land 71 

Water 70 

Volcanoes 49 

Earthquakes ,.. 52 

Animals 132 

Plants 128 

Man 135 

Marine Life 135 

Double Stars 150 

Earth 63 

Internal Heat of 46 

Interior 47, 54 

Form 63 

Size 64 

Density 64 

"Weight 64 

Motion 65 

Crust of 27,30,33,122 

Earthquakes 51,52, 53 

Causes of 52 

EcKpses , 145 

Ecliptic 67, 68, 143, 144 

Electrical Disturbances 20 

Electricity 19 

Atmospheric 20 

Accumulation of 22 

Energy 18 

Attractive 14 

Electric 19 

Kinetic 18 

Potential IS 

Volcanic 51, 52 

Eocene System 57 

Equator 14, 67 

Equinoxes 6G 

Ether 138 



PAGE 

Evaporation. ...;.... 115 

Exterior Planets 59, 142, 143 

Extinct Animals 57 

Faculse 62 

FaUing Stars 146 

Fixed Stars • 59 

Flora of Continents 130 

Flint 39 

Fog 117 

Foramiuif era 55 

Polyps 55 

Force 7 

Forces, Composition of 9 

Kesolution 

Parallelogram of 9, 10 

Polygon of 7, 11 

Fumaroles 51 

Gaseous Bodies 33 

Geodetic Surveys 159 

Geology 7, 35 

Geysers 51 

Glaciers 121, 122 

Alps 122, 123 

Globular Projection 160 

Granite 30 

Composition of 31, 43, 45 

Graptolites 56 

Gravel 37 

Gravitation ., 13, 16 

Gravity, Terrestrial 14 

Gregorian Telescopes 165 

Grit 36 

Gulf Stream 91,126 

Gypsum 42 

Han 121 

Hailstorms 121 

Heat 19, 20, 33, 36, 42, 43, 

46, 109, 110, 125, 126 
Heavenly Bodies, Distance of , . 142 

Herscheiian Telescope 165 

Hoar Frost 116 

Horizon 157 

Horse Latitudes 112 

Hot Springs 51 

Hottest Region 126 

Hurricanes 114 

Huxley's Classification 137 

Hydrogen 27, 33, 152, 154 

Hypsometrical Zones 129, 130 

Ice 34,121 

Ice, Ground 121 

Icebergs 123 

Ice Floes 124 

Igneous Rocks 43,44,37 



188 



INDEX. 



PAGE 

IncKnation of Earth's Axis " . . , . 65 

Magnetic Needle 25 

Indian Ocean 92 

Inland Seas 94 

Interior Planets 59 

Internal Heat of Globe 46 

Iran, Plateau of 81 

Islands 71, 72 

Volcanic 72 

Coral 72 

Isotheral Lines 126 

Isothermal 126, 128 

Isocheimal 126 



Japan Current 92 

Jupiter 59, 64, 142, 144, 156 

Jurassic System 55, 56 

Lakes 103 

Distribution 103 

Areas 103,104 

Uses of 104 

Land Breezes 113 

Landes 82 

Lanr) slips 122 

Latitude 67, 125, 157 

Lauren tian System 56 

Lenses 164 

Lias 57 



Life. 



128 

Animal 66,57,58,132 

Plant 12S, 129 

Light 62, 108, 137, 139, 151, 155 

Velocity 139 

Lightning 22 

Lignite 40 

Limestone 38, 39 

Coral 39 

Lines, Co-tidal 88 

Llanos 69 

Longitude 67,157 

Magnet, The Earth a 22 

Magnetic Needle 23, 25 

Inclination 23, 167 

Elements 24 

Declination 25 

Poles 21,23 

Storms 25 

Instruments 166 

Magnetism 22 

Terrestrial 22 

Mammals 57, 58, 132, 133, 134 

Man 58,135, 136 

M p Projections 159 

Mariner's Compass 23 



PAGB 

Marine Vegetation 130 

Life 135 

Zones 135 

Marl 37,38 

Mars 59, 141, 142, 143, 144 

Mass, Unit of 8 

Matter 12, 13,46 

Mean Elevation of Continents . , 74 

Mercury 59, 64, 142, 143 

Meridians 67 

Mesozoic Period 55 

Metamorphic Rocks 42 

Meteors 146 

Metric System 8 

Microscope 166 

Minor Planets 59, 141 

Miocene System 55, 57 

Mirage 109 

Mist 116 

Mistral 114 

Molecules 12 

Mongolian Race 136, 137 

Monsoons 112, 113 

Moon 47, 59, 61, 62, 142, 144 

Moraines 122 

Motion 8, 9, 59, 65, 66 

Mountains 45, 50, 74 

Mountain Systems 75 

Europe 75 

Asia 77 

Africa 78 

America 79 

Movements of Earth's Crust . .53, 54 

Of the Oceans 86 

Mud 37, 54 

Volcanoes 51 

Nadir 157 

NeapTides 88 

Nebulae 155 

N ebuldr Hypothesis 156, 16S 

Negro Race 136 

Neptune 59, 142. 115 

Newtonian Telescope 165 

Niagara Falls 58, 96 

Night 65,123, 124 

Nodes 66, 67 

Oceans 71, 84 

Density , 84 

Movements of 86 

Saltness 85 

Colour 86 

Bottom of 86 

0»d Red Sandstone 55, 56 

Oolitic System 55. 57 

Optical Instruments 152. 164 



INDEX. 



189 



PAGE 

Orbits of Planets. .59, 60, 142, 143, 144 

Organically-formed Rocks 38 

Oxygen 27,29, 30, 33 

PacificOcean 91 

Depth 91,92 

Temperatrire 92 

Currents 92 

Branches 92 

Pack-ice 124 

Palaeozoic Period 55 

Pampas 83, 114 

ParaUax 140, 141 

Peat 40 

Permian System 55, 56 

Pendiilum 8 

Photosphere 62, 152 

Physics , 7 

Physiography 7 

Placoids 56 

Plains 80, 82 

Planets 59,141, 144, 145 

Plants 54, 55, 128, 131 

Plateaux 80, 81 

Pliocene Formation 57 

Plutonic Rocks 45 

Polders 83 

Population of Globe 137 

Post-tertiary System 55, 58 

Precession of Equinoxes 66 

Precessional Motion 66 

Pressure 42, 45, 85 

Atmosphere 105 

Projections, Map 159 

Propagation of Light 139 

Protozoans , 132 

Puna Winds 114 

Quartz 3i 

Races 135 

Radiation '.*.'.'.'.'. 36,' 110,' I'l^ 125, 138 

Rain , 117, 122 

Rainbow 108 

Rainfall 117, 118 

Rainless Regions 119 

Rapids , , 95 

Rays of Light.. 108, 138, 140, 151, 154 

Reefs 53, 55 

Refiaction of Light 108 

Relative Age of Strata 54 

Reptiles 57,132,135 

Revolution of Apsides 66, 67 

Earth 65, 66 

Planets 142 

Elver Systems 97, 102 

Actinu on Earth's Surface 96, 122 

Basins 95 

Velocity QQ 



_ _ PAGE 

Rocks 35,36 

Composition of 31, 32, 33 

Saltin Ocean 85,86 

Sandstone 36 

SateUites 59, 61, 62, 145 

Density of 145 

Saturn 59,142,144, 156 

Sea-breezes 113 

Sea's Action on Earth's Crust . . 93 

Seas Inland 94 

Seasons 65, 143 

Sedimentary Rocks 36 

Shale 37 

Shingle 36, 37 

Shooting Stars 147 

Sihca 31, 33 

Silicon 28, 33 

Silurian System 56 

Size of Planets 142 

Slope 74 

Counter 74 

Snow 119, 122, 123 

Red 124 

Snowline 120 

Soil, Surface 38 

Composition of 38 

Fclar Day 7 

ParaUax 140, 141 

Spectrum 151 

Radiation 188 

System 59, 143, 147 

Salfataras 61 

Specific Gravity.... 47, 61, 64, 84, 142 

Spectroscope 62, 152, 156 

Spectrum Analysis 151, 156 

Spots, Sun 20, 61154, 155 

Springs 94, 95, 122 

Steppes 82 

Stars 59, 147 

Fixed 148, 151, 156 

Variable 149 

Coloured 149, 150 

Cold 149 

Stereographic Projection 159 

Storms 22, 25, 30, 114, 154, 155 

Stratified Rocks 36 

Subsidence 53 

Sun 59, 62 

Brightness of 62 

Composition 62,153 

Heat of 62 

Distance 141, 142 

Sizeof 142 

Densiiy.. 142 

Spots 20, 61, 154,155 

Surface Soil 38 

Surveys, Geodetical 162 



190 



INDEX. 



PAGR 

Tablelands ,..:;...'..:......... 80, 81 

Table of Minerals (rock-forming) 32 

Telescope 164 

Temperature of Atmosphere. 105, 109 

Oceans 90,93 

Planets 143 

Terrestrial Magnetism 22 

Tertiary System 55, 57 

Theodolite 162 

Thermal Springs 51 

Thermometer 109 

Rules 110 

Thunder 21, 22 

Tidal Wave 88 

Tides 87 

Spring and Neap 88 

Trade Winds Ill, 114 

Transmission of Light 108 

Heat 108 

Transportation of Rivers 96 

Triassic System 55, 56 

Trilobites 56 

Twilight 108, 124 

Typhoons 114 

CJnstratified Rocks 36 

Upheavals 53 

Dranus 59, 142, 144 

Valleys 80,82 

Vapour 115 

Variable Stars 149 



PAGB 

Vegetable Products 131, 139 

Vegetation, Marine 130 

Velocity 11,12 

OfLight 139 

Of Rivers 96 

Venus 59,141,142, 14S 

Volcanic Rocks 43 

Volcanoes 48 

Distribution 49 

Cause of 47, 48 

Water 33 

Several States 33 

of Land 94 

Waterfalls 96 

Waves 86 

Tidal 88 

Light 139 

Weight 13 

of Atmosphere 105 

Winds 110 

Trade Ill 

Periodical 112 

Variable 113 

Hot 113 

Cold 114 

Zenith 157 

Zodiacal Light 155 

Zones 68 

Botanical 128,129 

Hypsometrical 130 



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